v2.2-stable

This is version 2.2 of the PGD Community SDL2-for-Pascal Units.

Release notes:

• SDL2 unit is up-to-date with at least version 2.0.14 of the SDL2 library (exception sdlthread.inc)
• many aliases got replaced by typed enums
• add single and double pointers for all types (thanks furious-programming)
• update SDL_ttf.pas to latest version 2.21.0
• replace data types by c data types (see PR #29)
• add folder structure (see PR #27)
• many bugfixes

v2.1 Compatibility Release

Version 2.1 of the PGD Community SDL2 Headers
Release notes:

• This is a compatibility release. Use this release only if necessary. See remarks below.
• It has all commits until the point of adding a folder structure to the project and shifting the unit files into the units folder (see PR #27). Compare the disucssion in issue #22.
• Shifiting the units into the unit folder may (1) raise difficulties in committing new changes if the branch was started before and (2) make updates of project research pathes necessary.