The TreeParser requires information about a lot of the decoder's
current state in order to parse syntax tree elements correctly, so
there has to be some communication between the Decoder and the
TreeParser. Previously, the Decoder would copy its state to the
TreeParser when it changed, however, this was a poor choice. Now,
the TreeParser simply has a reference to its owning Decoder, and
accesses its state directly.
This patch adds compressed header parsing to the VP9 decoder (section
6.4 of the spec). This is the final decoder step before we can start to
decode tiles.
This patch brings all of the previous work together and starts to
actually parse and decode frame information. Currently it only parses
the uncompressed header data (section 6.2 of the spec).
