Use LibSoX instead of FFmpeg.

LibSoX is an audio decoding/encoding/effects library with a much cleaner and
high-level API than FFmpeg.  Using LibSoX makes the AudioSource much simpler
and easier to maintain, at the cost of making Playslave++ a bit more difficult
to build, as well as possibly dumping some more obscure sound formats.

LibSoX provides us with 32-bit unsigned packed samples, which are always
accepted by PortAudio, and this simplifies things a _lot_.  Gone is the need to
use a resampler.  Although we still have sample formats and lots of functions
for getting sample/byte rates, these can now feasibly be removed if considered
to be more bloat than useful abstraction.

This is an initial switch to LibSoX, and will probably eat your cat.  It needs
extensive testing before being merged in, but hopefully the resulting lighter
codebase will make bugs easier to detect.
Add some Visual Studio field notes.

LibSoX makes the VS build a bit more complicated, so I've added these into the
tree to compensate.

These are slightly cobbled together from memory, and may be a bit incorrect or
incomplete in areas.  If people could try out VS builds and fix up issues in
the notes, this would be great.
Merge recent clang-format changes.

This should have been done at the start (as a rebase), but I forgot.  Silly me.
Remove last vestiges of ffmpeg in source.

Thanks to @LordAro for pointing these out
Update Makefile to use libsox.

This also switches the default CC/CXX back to clang/clang++, because
why not.
Some missing includes with linux
Update readme for libsox, add minimal osx info
Add FreeBSD information to readme and reformat.

Here's a readme
There's a readme
And another little readme
Fuzzy readme
Funny readme
Readme readme doc.
Remove `@freebsd` from FreeBSD docs.

This makes Doxygen upset.
Add up some details
Merge pull request #24 from UniversityRadioYork/libsox

LibSoX migration