Implement huffman decoding using code from twitter/hpack

DO NOT MERGE:

Just throwing this up for initial feedback, as I haven't backfilled scenario tests.  That said, using this code will work against https://twitter.com

### Overview
This implements huffman decoding using a modified version of classes from [Twitter Hpack](https://github.com/twitter/hpack).  We will need to change these a bit more to avoid creating excess byte arrays.

cc @jpinner (ps Thanks!)