* Remove opl_sample_rate variable since it has no practical effect
* Deactivate idle OPL chips
Allocate free OPL voices from active chips before inactive ones
* Add comments for new constants
* Ensure OPL chip LFOs are kept in sync after dormancy
* Check for chip activations before sample generation to preserve sync
* Use correct OPL3 channel polarity by default
* Support multiple OPL3 chips
* Use native OPL sample rate and allow OpenAL to resample it
* Bind DMX OPL stereo correction to a config variable; default to vanilla
* Consolidate num_opl_chips variables; remove menu item
Use BETWEEN macro for mix clamping
* Disable upper register banks when dmx is in OPL2 mode
* Forward declaration of structures in headers where possible
* Use M_snprinf instead of sprintf
* Remove D_INTMAX D_INTMIN
* Don't change libtextscreen files
* Add miniz and win32 include directories
* implement M_getenv for compatibility with non-Latin paths on Windows
* use regular wcslen
SDL_wcslen is undocumented
* fix memory leak
* cache the `wenv == NULL` case
* add OPL emulation from Chocolate Doom
* get rid of detect_voices
* split the SDL music backend into a separate source file
* add post-realloc() check
* add OPL emulation copyright holders
* add some minimal comments
* add config variable and menu item
* sacrifice PCX format screenshot menu entry
