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 month. Most important changes:

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.

brotli/dec/decode.h

@@ -26,6 +26,8 @@ extern "C" {
 #endif
 
 /* Sets *decoded_size to the decompressed size of the given encoded stream. */
+/* This function only works if the encoded buffer has a single meta block, */
+/* and this meta block must have the "is last" bit set. */
 /* Returns 1 on success, 0 on failure. */
 int BrotliDecompressedSize(size_t encoded_size,
                            const uint8_t* encoded_buffer,