Becoming truly open source

This update is more of a technicality.

After many years, the author of Blitz 3d has started supplying updates again. One of these removes the dependency to the FMOD sound library. This is great as there were licensing issues with FMOD, which rendered the game’s GitHub repository technically non-open-source.

Also, the update brings some small code improvements. It is compiled with a modernized version of Blitz3d; so it might generate technical issues, but more probably, it should increase compatibility.