HTTP/2 Data Decompression

Motivation:
The HTTP/2 codec does not provide a way to decompress data. This functionality is supported by the HTTP codec and is expected to be a commonly used feature.

Modifications:
-The Http2FrameReader will be modified to allow hooks for decompression
-New classes which detect the decompression from HTTP/2 header frames and uses that decompression when HTTP/2 data frames come in
-New unit tests

Result:
The HTTP/2 codec will provide a means to support data decompression
Rename to `nextReadableBuf` ?