Refactored Audio into JackAudio and AlsaAudio

To make it cleaner to add a new kind of Audio, for OSX
(probably PortAudio)

Needs to be tested on linux still, but seems to work for Jack.
PortAudio support in OSX

PortAudio, and it works. This makes no-hassle sound on OSX, if all you
want is sound. It may survive laptop sleep cycles too (though I haven't
tried it yet), and plugging/unplugging external sound cards (like any other
native osx app).

TODO:
- Smarter parameter selection.
- Maybe they want to use PA on Linux too.
- What about Windows? Do we even want to try going there?
- Maybe people don't want to depend on JACK at all, make the build process
  JACK-optional.