Merge RFC4 (#1865)

This commit is the result of the squashing of rfc4_dev branch in a single
commit. It implements mostly RFC 4 related work.

* Grid handling:
  - remove obsolete and presumably unfinished implementation of grid catalog functionality
  - all grid functionality is in grids.cpp/.hpp
  - vertical and horizontal grid shift: rework to no longer load whole grid into memory
  - remove hgrids and vgrids member from PJ structure, and store them in hgridshift/vgridshift/deformation structures
  - build systems: add optional libtiff dependency. Must be explicitly disabled if not desired
  - add support for horizontal and vertical grids in GeoTIFF, if libtiff is available
  - add GenericShiftGridSet and GenericShiftGrid classes, relying on TIFF grids, that can be used for generic purpose grid-based adjustment
  - add a +proj=xyzgridshift method to perform geocentric translation by grid. Used for French NTF to RGF93 transformation using gr3df97a.tif grid
  - deformation: add support for +grids= for GeoTIFF grids
  - horizontal grid shift: fix failures on points slightly outside a subgrid (fixes #209)

* File management:
  - add a filemanager.cpp/.hpp to deal with file related work
  - test for legacy proj_api.h fileapi
  - proj.h: add proj_context_set_fileapi() and proj_context_set_sqlite3_vfs_name() (fixes #866)
  - add capability to read resource files from the user writable directory

* Network access:
  - build systems: add optional curl dependency
  - add a curl-based default implementation for network related functionality
  - proj.h: add C API to control network functionality, and optionaly provide network callbacks
  - add data/proj.ini with default settings
  - add a SQLite3 local cache of downloaded chunks
  - add proj_is_download_needed() and proj_download_file()

* Use Win32 Unicode APIs and expect all strings to be UTF-8 (fixes #1765)
  For backward compatibility, if PROJ_LIB content is found to be not UTF-8 or
  pointing to a non existing directory, then an attempt at interpretating it
  in the ANSI page encoding is done.
  proj_context_set_search_paths() now assumes strings to be in UTF-8, and
  functions returning paths will also return values in UTF-8.

11 files changed, 96 insertions, 11 deletions

diff --git a/docs/source/development/reference/cpp/common.rst b/docs/source/development/reference/cpp/common.rst
index c1a28d37..4e92f6b2 100644
--- a/docs/source/development/reference/cpp/common.rst
+++ b/docs/source/development/reference/cpp/common.rst
@@ -4,5 +4,5 @@ common namespace
 ----------------
 
 .. doxygennamespace:: osgeo::proj::common
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/cpp_general.rst b/docs/source/development/reference/cpp/cpp_general.rst
index 3b47d01e..d54daaa8 100644
--- a/docs/source/development/reference/cpp/cpp_general.rst
+++ b/docs/source/development/reference/cpp/cpp_general.rst
@@ -4,4 +4,4 @@ General documentation
 ---------------------
 
 .. doxygenfile:: general_doc.dox.reworked.h
-   :project: cpp_stuff
+   :project: doxygen_api
diff --git a/docs/source/development/reference/cpp/crs.rst b/docs/source/development/reference/cpp/crs.rst
index 2abea378..f8df118e 100644
--- a/docs/source/development/reference/cpp/crs.rst
+++ b/docs/source/development/reference/cpp/crs.rst
@@ -4,5 +4,5 @@ crs namespace
 -------------
 
 .. doxygennamespace:: osgeo::proj::crs
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/cs.rst b/docs/source/development/reference/cpp/cs.rst
index b168213f..376ae6a6 100644
--- a/docs/source/development/reference/cpp/cs.rst
+++ b/docs/source/development/reference/cpp/cs.rst
@@ -4,5 +4,5 @@ cs namespace
 ------------
 
 .. doxygennamespace:: osgeo::proj::cs
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/datum.rst b/docs/source/development/reference/cpp/datum.rst
index 1fee5f8a..0a545a68 100644
--- a/docs/source/development/reference/cpp/datum.rst
+++ b/docs/source/development/reference/cpp/datum.rst
@@ -4,5 +4,5 @@ datum namespace
 ---------------
 
 .. doxygennamespace:: osgeo::proj::datum
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/io.rst b/docs/source/development/reference/cpp/io.rst
index 9da0f680..9729af90 100644
--- a/docs/source/development/reference/cpp/io.rst
+++ b/docs/source/development/reference/cpp/io.rst
@@ -4,5 +4,5 @@ io namespace
 ------------
 
 .. doxygennamespace:: osgeo::proj::io
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/metadata.rst b/docs/source/development/reference/cpp/metadata.rst
index b3960122..348627e8 100644
--- a/docs/source/development/reference/cpp/metadata.rst
+++ b/docs/source/development/reference/cpp/metadata.rst
@@ -4,5 +4,5 @@ metadata namespace
 ------------------
 
 .. doxygennamespace:: osgeo::proj::metadata
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/operation.rst b/docs/source/development/reference/cpp/operation.rst
index bc3f201d..88096cb8 100644
--- a/docs/source/development/reference/cpp/operation.rst
+++ b/docs/source/development/reference/cpp/operation.rst
@@ -4,5 +4,5 @@ operation namespace
 -------------------
 
 .. doxygennamespace:: osgeo::proj::operation
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/cpp/util.rst b/docs/source/development/reference/cpp/util.rst
index 1aba2954..bc9676a4 100644
--- a/docs/source/development/reference/cpp/util.rst
+++ b/docs/source/development/reference/cpp/util.rst
@@ -4,5 +4,5 @@ util namespace
 --------------
 
 .. doxygennamespace:: osgeo::proj::util
-   :project: cpp_stuff
+   :project: doxygen_api
    :members:
diff --git a/docs/source/development/reference/datatypes.rst b/docs/source/development/reference/datatypes.rst
index 18bd7efd..7ec17eb1 100644
--- a/docs/source/development/reference/datatypes.rst
+++ b/docs/source/development/reference/datatypes.rst
@@ -797,11 +797,48 @@ Logging
     .. versionadded:: 5.1.0
 
 
+Setting custom I/O functions
+-------------------------------------------------------------------------------
+
+.. versionadded:: 7.0.0
+
+.. doxygenstruct:: PROJ_FILE_API
+   :project: doxygen_api
+   :members:
+
+.. doxygentypedef:: PROJ_FILE_HANDLE
+   :project: doxygen_api
+
+.. doxygenenum:: PROJ_OPEN_ACCESS
+   :project: doxygen_api
+
+
+Network related functionality
+-------------------------------------------------------------------------------
+
+.. versionadded:: 7.0.0
+
+.. doxygentypedef:: PROJ_NETWORK_HANDLE
+   :project: doxygen_api
+
+.. doxygentypedef:: proj_network_open_cbk_type
+   :project: doxygen_api
+
+.. doxygentypedef:: proj_network_close_cbk_type
+   :project: doxygen_api
+
+.. doxygentypedef:: proj_network_get_header_value_cbk_type
+   :project: doxygen_api
+
+.. doxygentypedef:: proj_network_read_range_type
+   :project: doxygen_api
+
+
 C API for ISO-19111 functionality
 -------------------------------------------------------------------------------
 
 .. doxygengroup:: iso19111_types
-   :project: cpp_stuff
+   :project: doxygen_api
    :content-only:
 
 
diff --git a/docs/source/development/reference/functions.rst b/docs/source/development/reference/functions.rst
index c010fd13..a2a0c3ae 100644
--- a/docs/source/development/reference/functions.rst
+++ b/docs/source/development/reference/functions.rst
@@ -697,6 +697,54 @@ Various
     :returns: :c:type:`int` 1 if output units is expected in radians, otherwise 0
 
 
+Setting custom I/O functions
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+.. versionadded:: 7.0.0
+
+.. doxygenfunction:: proj_context_set_fileapi
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_context_set_sqlite3_vfs_name
+   :project: doxygen_api
+
+
+Network related functionality
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+.. versionadded:: 7.0.0
+
+.. doxygenfunction:: proj_context_set_network_callbacks
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_context_set_enable_network
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_context_set_url_endpoint
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_grid_cache_set_enable
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_grid_cache_set_filename
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_grid_cache_set_max_size
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_grid_cache_set_ttl
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_grid_cache_clear
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_is_download_needed
+   :project: doxygen_api
+
+.. doxygenfunction:: proj_download_file
+   :project: doxygen_api
+
+
 Cleanup
 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
@@ -727,6 +775,6 @@ which are not of type CRS (can be tested with :c:func:`proj_is_crs`),
 will return an error when used with functions of this section.
 
 .. doxygengroup:: iso19111_functions
-   :project: cpp_stuff
+   :project: doxygen_api
    :content-only: