style cleanups and an ERRQUIT
bugfix: save/restore state before C routine
renamed for clarity
Add speaker and soundcore targets
macro refactoring for clarity [sic]
Timing model back to nanosleep for sound fidelity

This is part 1 of 2

    * Proper emulator timing is critical for emulating the Apple2 speaker with a
      square wave on a modern soundcard.  The AppleWin sources provided
      reference, inspiration, and source for both timing and speaker emulation
      code.

    * cpu.S, cpu.h, timing.c : OK so I flip-flopped quite a bit here on how best
      to do proper emulator timing, but the previous spinloop implementation was
      not one of my more enlightened decisions :P ... cpu/power consumption
      nightmare ...

    * ds-shim.h, win-shim.h -- Shims for Windows-isms and DirectSound-isms.  I
      assume these will eventually be refactored away...

    * soundcore.[hc], speaker.[hc] -- Directly ported from a recent version of
      AppleWin.  Everything I've added should be braced with #ifdef APPLE2IX.

    * soundcore-alsa.[hc] -- An ALSA backend using mmap'ed soundcard access.