plugins/id3: Add new fields

plugins/id3: Add new fields

Add codec, sampling rate and channels. Container is left empty on
purpose since .mp3 and .aac files are not inside a container per se. We
may want to split the _codecs table later and put the first part as the
container.

We also have basic support for AAC file in a MPEG 4 file, since it's
almost the same of an MPEG2 one.

We only parse audio parameter fields for the ones with ADTS header.
Adding support for ADIF shall be trivial in the future. The current code
find the ID3v2 tag is actually doing more than it needed. The only case
in which the ID3 tag would not be in the start of the file is if there
was an ADIF tag first. But then the header has a fixed size and we
shouldn't need to use a ring buffer of 3 chars. When adding support to
ADIF we may want to kill useless code.

Regarding the supported codecs, we support all the
mpeg{1,2,2.5,3}layer{1,2,3} values. For AAC there's MAIN, LC, SSR and
LTP. Both for MPEG 2 and 4.