This is the first release of dav1d, the fast and small AV1 decoder,
codename 'Gazelle'.

It supports all AV1 features and all bitdepths, from 8 to 12bits, and all subsamplings.
It is very fast compared to other AV1 decoders on AVX-2 processors.

It has already SSSE3 and NEON code for other processors, and will get a
lot more of those optimizations in the future.