* include/codecs.h: new header file to store information shared by decoders
   and demuxers, like the BITMAPINFOHEADER structure for instance.
* modules/demux/ogg.c: the ogg demuxer should now work nicely with ogm files
   (including for the video). It has only been tested with a few streams
   produced with dvd::rip and ogmmerge though.