undefined shift behaviour.
Document this, fix the assert and add a put_bits32 to handle writing 32
bits and use that where necessary.
Originally committed as revision 20124 to svn://svn.ffmpeg.org/ffmpeg/trunk
improve plain text doxy readability.
See the thread: "[RFC] Should we use doxygen markup?".
Originally committed as revision 19122 to svn://svn.ffmpeg.org/ffmpeg/trunk