HTTP/2 Draft 15

Motivation:
A new draft of the HTTP/2 spec has been released.

Modifications:
Make updates as defined in https://tools.ietf.org/html/draft-ietf-httpbis-http2-15

Result:
HTTP/2 codec is draft 15 compliant.
I can remove.  I had a bunch of try{}catch{} blocks for each statement and so the variables were final oustide the try/catch.  Now that I consolidated all the try/catch logic into 1 block I can remove the final on these.