Version 2.0.4

Bugfix:
- Fix memory allocation for PostgreSQL 12 and above (Julien Rouhaud)
- Fix bug when append plans are empty (Ronan Dunklau)
Miscellaneous:
- Fix a faulty strncpy() call (Julien Rouhaud, per report from github user RekGRpth)
- Fix some cppcheck warnings (Julien Rouhaud, per report from github user RekGRpth)
- Improve extension ugprade documentation (Julien Rouhaud)
- Make sure the code can be compiled and used on Windows (Julien Rouhaud, per report from github user suprimex)
- Add compatibility with PostgreSQL 15 (Julien Rouhaud)