Add contributors file.
Make README rst.
Rename contributors.rst to CONTRIBUTORS.rst
Manage the reference set better.

HPACK relies on streaming decoding. This means that things may be
added to the header table and then removed from it in the same
header block. When things are removed from the header table, they
should also be removed from the reference set.

The combination of these two facts means that we cannot rely on
the reference set containing all headers emitted during processing
of the current header block. We need to more aggressively return
headers from our processing functions, and rely on the set logic
to prevent us duplicating them.

This causes all current HPACK decoder integration tests to pass.

There is a similar set of changes required for the HPACK encoder,
but we'll wait until we have a good set of encoder integration
tests first.
Test for using bytes internally.
Change the static tables to bytes.
Unicode at the edges.

The Encoder and Decoder classes currently use Unicode strings
throughout. This seemed reasonable at the time they were
originally written: it seemed sensible to have the interface to
bytes at the bottom of these classes, not the top. However,
becuase the entire HPACK spec defines headers in terms of octet
sequences, we had a lot of very costly operations. In the worst
cases, we had a linear 2n cost each time we calculated the size of
the header table, as we had to encode every header name and value.
Because we calculated the size of the header table every time we
encoded/decoded a header, this led to a whopping 2nm flat overhead
that could be totally avoided if we simply encoded headers as they
came in and decoded them as they went out.

This change moves the bytes interface to the top of the class,
replacing our 2nm cost with a single 2m, where m is usually << n.
Tests should use binary strings.
Fixup some broken test strings.
Hex to bin works on unicode strings: don't need it.

The Huffman decoder will work on binary strings.
Move the removal of the binary prefix.
Docstrings for all.
Should return bytestrings.
Work with bytes, not text.
Add @elricL to contributors.
Huffman encoding with tests