This patch builds on my previous DFPWM codec patch, adding a raw
audio format to be able to read/write the raw files that are most commonly
used (as no other container format supports it yet).

The muxers are mostly copied from the PCM demuxer and the raw muxers, as
DFPWM is typically stored as raw data.

Please see the previous patch for more information on DFPWM.
Signed-off-by: Jack Bruienne <jackbruienne@gmail.com>