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.

1 files changed, 9 insertions, 0 deletions

diff --git a/docs/source/references.bib b/docs/source/references.bib
index 529c20e1..13853764 100644
--- a/docs/source/references.bib
+++ b/docs/source/references.bib
@@ -229,6 +229,15 @@
   Doi                      = {10.2312/PE/PG/PG2012short/005-010}
 }
 
+@TechReport{NTF_88,
+  Title                    = {Grille de parametres de transformation de coordonnees - {GR3DF97A} - Notice d'utilisation},
+  Author                   = {IGN},
+  Institution              = {Service de Geodesie et Nivellement, Institut Geographique National},
+  Year                     = {1997},
+
+  Url                      = {https://geodesie.ign.fr/contenu/fichiers/documentation/algorithmes/notice/NTG_88.pdf}
+}
+
 @TechReport{ONeilLaubscher1976,
   Title                    = {Extended Studies of a Quadrilateralized Spherical Cube Earth Data Base},
   Author                   = {E. M. O'Neill and R. E. Laubscher},