Circumvent filter_new() with a fake ConfigBlock.

struct AudioOutput should not know or care about multi-threading.

Was broken by commit 8a86460b

Closes #87

Addresses #82.

Previously, the ffmpeg decoder only checked for the "generic"
MusicBrainz metadata keys used in other metadata container formats.

We will reuse these tags elsewhere.

Enable it in the Windows build script, closes #78.

LAME currently doesn't support Android:

 checking host system type... Invalid configuration `arm-linux-androideabi': system `androideabi' not recognized