This work mostly consists of:
- a C++ implementation of the ISO-19111:2018 / OGC Topic 2
"Referencing by coordinates" classes to represent Datums,
Coordinate systems, CRSs (Coordinate Reference Systems) and
Coordinate Operations.
- methods to convert between this C++ modeling and WKT1, WKT2
and PROJ string representations of those objects
- management and query of a SQLite3 database of CRS and Coordinate Operation definition
- a C API binding part of those capabilities
This is all-in-one squashed commit of the work of
https://github.com/OSGeo/proj.4/pull/1040
