Simple and portable single file AV1 OBU parser written in mostly C89 with a
tiny bit of C99.

*  No allocations; only works on user-provided buffers and the stack.
*  OBU header parsing.
*  Sequence Header OBU parsing.
*  Metadata OBU parsing.
*  Tile List OBU parsing.
*  Tile Group OBU parsing.
*  Frame Header OBU parsing.
*  Frame OBU parsing.