Add proj_grid_get_info_from_database

[nyalldawson]

Allows retrieval of grid metadata from a grid filename. Currently the only way to retrieve this is via proj_coordoperation_get_grid_used, but that requires an existing coordinate operation object (which can be impossible to create if a particular grid is not locally available).

[nyalldawson]

@rouault done!

[kbevers]

Complaint from Travis:

proj_get_source_crs
 proj_get_target_crs
 proj_get_type
+proj_grid_get_info_from_database
 proj_grid_info
 proj_identify
 proj_info
Difference(s) found in exported symbols. If intended, refresh scripts/reference_exported_symbols.txt with 'scripts/dump_exported_symbols.sh src/.libs/libproj.so > scripts/reference_exported_symbols.txt'
The command "./travis/${BUILD_NAME}/install.sh" failed and exited with 1 during .

Error message explains what to do :)

[nyalldawson]

@kbevers thanks, fixed