Updates to Brotli compression format, decoder and encoder This commit contains a batch of changes that were made to the Brotli compression algorithm in the last three weeks. Most important changes: * Added UTF8 context model for good text compression. * Simplified context modeling by having only 4 context modes. * Per-block context mode selection. * Faster backward copying and bit reading functions. * More efficient histogram coding. * Streaming support for the decoder and encoder.