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.

3 files changed, 28 insertions, 3 deletions

diff --git a/docs/source/apps/cct.rst b/docs/source/apps/cct.rst
index a4cc690c..96b5f13b 100644
--- a/docs/source/apps/cct.rst
+++ b/docs/source/apps/cct.rst
@@ -91,6 +91,17 @@ cartesian coordinates) and
 *Coordinate Transformations*, which are coordinate operations where
 input and output datums differ (e.g. change of reference frame).
 
+Use of remote grids
+*******************
+
+.. versionadded:: 7.0.0
+
+If the :envvar:`PROJ_NETWORK` environment variable is set to ``ON``,
+:program:`cct` will attempt to use remote grids stored on CDN (Content
+Delivery Network) storage, when they are not available locally.
+
+More details are available in the :ref:`network` section.
+
 Examples
 ********
 
diff --git a/docs/source/apps/cs2cs.rst b/docs/source/apps/cs2cs.rst
index 12f91e64..c95bbaed 100644
--- a/docs/source/apps/cs2cs.rst
+++ b/docs/source/apps/cs2cs.rst
@@ -171,6 +171,16 @@ normally be in DMS format (use ``-f %.12f`` for decimal degrees with 12 decimal
 places), while projected (cartesian) coordinates will be in linear
 (meter, feet) units.
 
+Use of remote grids
+-------------------
+
+.. versionadded:: 7.0.0
+
+If the :envvar:`PROJ_NETWORK` environment variable is set to ``ON``,
+:program:`cs2cs` will attempt to use remote grids stored on CDN (Content
+Delivery Network) storage, when they are not available locally.
+
+More details are available in the :ref:`network` section.
 
 Examples
 ********
diff --git a/docs/source/apps/projinfo.rst b/docs/source/apps/projinfo.rst
index d1889844..47deaaeb 100644
--- a/docs/source/apps/projinfo.rst
+++ b/docs/source/apps/projinfo.rst
@@ -20,7 +20,7 @@ Synopsis
     |    [[--area name_or_code] | [--bbox west_long,south_lat,east_long,north_lat]]
     |    [--spatial-test contains|intersects]
     |    [--crs-extent-use none|both|intersection|smallest]
-    |    [--grid-check none|discard_missing|sort] [--show-superseded]
+    |    [--grid-check none|discard_missing|sort|known_available] [--show-superseded]
     |    [--pivot-crs always|if_no_direct_transformation|never|{auth:code[,auth:code]*}]
     |    [--boundcrs-to-wgs84]
     |    [--main-db-path path] [--aux-db-path path]*
@@ -151,12 +151,13 @@ The following control parameters can appear in any order:
 
     .. note:: only used for coordinate operation computation
 
-.. option:: --grid-check none|discard_missing|sort
+.. option:: --grid-check none|discard_missing|sort|known_available
 
     Specify how the presence or absence of a horizontal or vertical shift grid
     required for a coordinate operation affects the results returned when
     researching coordinate operations between 2 CRS.
-    The default strategy is ``sort``: in that case, all candidate
+    The default strategy is ``sort`` (if :envvar:`PROJ_NETWORK` is not defined).
+    In that case, all candidate
     operations are returned, but the actual availability of the grids is used
     to determine the sorting order. That is, if a coordinate operation involves
     using a grid that is not available in the PROJ resource directories
@@ -166,6 +167,9 @@ The following control parameters can appear in any order:
     this returns the results as if all the grids where available.
     The ``discard_missing`` strategy discards results that involve grids not
     present in the PROJ resource directories.
+    The ``known_available`` strategy discards results that involve grids not
+    present in the PROJ resource directories and that are not known of the CDN.
+    This is the default strategy is :envvar:`PROJ_NETWORK` is set to ``ON``.
 
     .. note:: only used for coordinate operation computation