ARS-emu version 0.6-alpha

The last expected hardware change has been made: stereo! And, when you give a mouse a cookie...

• Basic controller support has been added. @AdmiralPotato tricked me into doing it (by asking very nicely for it).
• Stereo mixing. APU voices may now be panned center/left/right/"boosted". Believe it or not, the ability to boost triangle waves was the killer app for this feature, not the stereo mixing per se...
• The sound code no longer requires SDL 2.0.4 or later. ARS-emu will now work back as far as 2.0.2. The change comes with a new, super spiffy automatic clock skew compensator.
• Specific support for headphones, quadraphonic sound, and 3.1/4.0/5.1/7.1 surround sound has been added. The quadraphonic and surround modes are untested.
• The Audio submenu of the configuration screen is now functional. (Next stop, video!)
• ROMs that embed SimpleConfig may now use it to configure the emulator without requiring that pesky -C option. (-C is still required to run nonstandard configuration code, though, just to be properly paranoid.)