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.
Hum I'm not so sure.  That is how I was interpreting the draft changes....

[section-5.3.1](https://tools.ietf.org/html/draft-ietf-httpbis-http2-16#section-5.3.1)
>A stream that depends on another stream is a dependent stream.  The
   stream upon which a stream is dependent is a parent stream.  A
   dependency on a stream that is not currently in the tree - such as a
   stream in the "idle" state - results in that stream being given a
   default priority (Section 5.3.5).


[section-5.3.4](https://tools.ietf.org/html/draft-ietf-httpbis-http2-16#section-5.3.4)
>Similarly, streams that are in the "idle" state can be assigned
   priority or become a parent of other streams.  This allows for the
   creation of a grouping node in the dependency tree, which enables
   more flexible expressions of priority.  Idle streams that are made a
   parent of another stream are assigned a default priority
   (Section 5.3.5).

WDYT?