The rawaudio demuxer had a rather hard to use way to set the audio
format with the --rawaudio=format=value option. The user had to pass a
numeric value, which then was set as wFormatTag member in the
WAVEFORMATEX header.
Make it use the mplayer audio format (the same as --af=format=value).
Add a new internal pseudo audio codec tag, which is hopefully unused,
which makes ad_pcm use the value in wFormatTag as internal mplayer
audio format.
Playing non-PCM formats is disabled. (At least AC3 can be played
directly.)
af_format.h declares some symbols which are defined in format.c. The
fact that af_format.c is a completely unrelated file is rather
confusing. Having the header and implementation file use the same base
name is more uniform. (af_format.c is the audio conversion filter, while
af_format.h and format.c are about audio formats and their properties.)
Also fix all source files which include this file.
