HTTP/2 Draft 16

Motivation:
HTTP/2 draft 16 has been released https://tools.ietf.org/html/draft-ietf-httpbis-http2-16.

Modifications:
The HTTP/2 codec should be updated to support draft 16.

Result:
HTTP/2 codec is draft 16 compliant.
Reading your other comments it looks like you are suggesting that we restructure the `createStream(..)` such that the caller is responsible for invoking some type of `open*()` method to initialize the state.  I think this makes sense.  Let me take a stab at this.