libmpq is a much simpler alternative to StormLib for reading MPQ archives.
We use our own fork of libmpq: https://github.com/diasurgical/libmpq
Impact:
* DevilutionX is now a lot more portable. Unlike StormLib, libmpq only
needs platform-specific code for Windows.
* Locks around file access **removed** (instead we duplicate the file descriptor for streamed audio only).
* RAM usage is **300 KiB** lower than StormLib.
* Stripped release linux_x86_64 binary is **32 KiB** smaller.
* Amiga build now hangs instead of crashing.
When playing the same sound twice with in a short duration then the
sound it self, the secound request would go unfulfilled. The solution is
to simply rewind the stream pointer before requesting a playback.
SDL_mixer can only stream a single music track
SDL_audiolib has unlimited streams.
With this change, we finally have streaming sounds (respecting
sfx_STREAM).
Audio options can now also be set via diablo.ini, which should help us
better diagnose the static noise issues.
