This command adds `ifversion`, as both a simplified and internal
command.
The system works like so:
- `ifversion(2.6,script2)` -> If you're on 2.6.0 or greater
- `ifversion(2.6.0,script2)` -> Same as above
- `ifversion(2.6.3,script2)` -> You're using 2.6.3 or greater
- `ifversion(2.5,script2)` -> You're using 2.5 or greater
- `ifversion(2,script2)` -> You're using 2.0.0 or greater (yep...)
`ReleaseVersion.h` has a few new defines to make this possible, being
`MAJOR_VERSION`, `MINOR_VERSION` and `PATCH_VERSION`. With the help of
a few macros, `RELEASE_VERSION` is now constructed using those.
I'm fine with putting the release version in a header file, thus
necessitating the need to recompile every file that includes it if it's
changed, simply because it's not supposed to be changed that often.
The SDL_arraysize is necessary because sometimes we'll have subreleases
(e.g. 2.4.1, 2.4.2, 2.4.3), and who knows, maybe we'll get to 2.10
someday.
