Dispatch content of 4D_api.cpp into multiple .cpp files

No functional change, just moving code around.

4D_api.cpp has become quite large and a set of 'random' things, that
didn't correlate well with the '4D' naming. Some re-organization was needed.

Create following files:
- src/area.cpp: PJ_AREA related code
- src/coordinates.cpp: functions related to coordinate manipulation
- src/coord_operation.cpp: PJCoordOperation methods
- src/create.cpp: pj_create_internal() related stuff
- src/crs_to_crs.cpp: proj_create_crs_to_crs() and the like
- src/dist.cpp: distance related functions
- src/info.cpp: proj_info() and proj_pj_info()
- src/trans.cpp: proj_trans(), proj_trans_array(), proj_trans_generic(), proj_roundtrip()
- src/trans_bounds.cpp: proj_trans_bounds()

Some other functions also moved to more relevant existing source files.

Doxyfile

@@ -766,7 +766,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = src/iso19111 src/iso19111/operation include/proj src/proj.h src/proj_experimental.h src/general_doc.dox src/filemanager.cpp src/networkfilemanager.cpp src/4D_api.cpp
+INPUT                  = src/iso19111 src/iso19111/operation include/proj src/proj.h src/proj_experimental.h src/general_doc.dox src/filemanager.cpp src/networkfilemanager.cpp src/coordinates.cpp src/trans_bounds.cpp
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses

scripts/doxygen.sh

@@ -40,7 +40,7 @@ fi
 
 rm -rf docs/build/xml/
 
-(cat Doxyfile; printf "GENERATE_HTML=NO\nGENERATE_XML=YES\nINPUT= src/iso19111 src/iso19111/operation include/proj src/proj.h src/filemanager.cpp src/networkfilemanager.cpp src/4D_api.cpp src/general_doc.dox") | doxygen -  > docs/build/docs_log.txt 2>&1
+(cat Doxyfile; printf "GENERATE_HTML=NO\nGENERATE_XML=YES\nINPUT= src/iso19111 src/iso19111/operation include/proj src/proj.h src/filemanager.cpp src/networkfilemanager.cpp src/coordinates.cpp src/trans_bounds.cpp src/general_doc.dox") | doxygen -  > docs/build/docs_log.txt 2>&1
 if grep -i warning docs/build/docs_log.txt; then
     echo "Doxygen warnings found" && cat docs/build/docs_log.txt && /bin/false;
 else