on2avc: Remove pointless dsputil.h #include
h264_picture: Remove pointless dsputil.h #include
dsputil: Split off HuffYUV decoding bits into their own context

Also shorten HuffYUV context member names to avoid clutter.
dsputil: Split off HuffYUV encoding bits into their own context

Also shorten HuffYUV context member names to avoid clutter.
oggenc: Move ogg_write_pages up above ogg_write_header

Signed-off-by: Martin Storsjö <martin@martin.st>
oggenc: Flush after writing headers

Before, header information for ogg format files was sent with the
first encoded packet.

This patch makes it so that it is possible for API users to
differentiate between headers and encoded audio. This is useful, for
example, when creating an audio stream where you want to send one set
of headers for every client that connects and then the encoded stream
of audio.

Signed-off-by: Martin Storsjö <martin@martin.st>