Push updates to the Brotli encoder and decoder upstream.

This commit contains a batch of changes that were made to the
Brotli library since March 2014. Most important changes:

* Fix BrotliDecompressedSize() to work for an uncompressed plus an
  empty meta-block.
* Move serialization functions into their own file.
* Fix storing of the meta-block header for last empty meta-block.
* Add a fast version of the hasher.