[#2642] CompositeByteBuf.deallocate memory/GC improvement

Motivation:

CompositeByteBuf.deallocate generates unnecessary GC pressure when using the 'foreach' loop, as a 'foreach' loop creates an iterator when looping.

Modification:

Convert 'foreach' loop into regular 'for' loop.

Result:

Less GC pressure (and possibly more throughput) as the 'for' loop does not create an iterator
Upgrade to HTTP/2 draft 13

Motivation:

Need to upgrade HTTP/2 implementation to latest draft.

Modifications:

Various changes to support draft 13.

Result:

Support for HTTP/2 draft 13.
[#2647] Respect IOV_MAX when call writev in native transport

Motivation:

epoll transport fails on gathering write of more then 1024 buffers. As linux supports max. 1024 iov entries when calling writev(...) the epoll transport throws an exception.

Thanks again to @blucas to provide me with a reproducer and so helped me to understand what the issue is.

Modifications:

Make sure we break down the writes if to many buffers are uses for gathering writes.

Result:

Gathering writes work with any number of buffers
Fix JVM segfault during JNI call. Part of [#2647]

Motivation:
Currently when Native.writev(...) is used it is possible to see a JVM segfault because the offset is updated to early.

Modification:
Only update the offset once it is safe to do so.

Result:
No more segfault
Moved bit-level read operations from Bzip2Decoder to the new Bzip2BitReader

Motivation:

Collect all bit-level read operations in one class is better. And now it's easy to use not only in Bzip2Decoder. For example, in Bzip2HuffmanStageDecoder.

Modifications:

Created a new class - Bzip2BitReader which provides bit-level reads.
Removed bit-level read operations from Bzip2Decoder.
Improved javadoc.

Result:

Bzip2BitReader allows the reading of single bit booleans, bit strings of arbitrary length (up to 24 bits), and bit aligned 32-bit integers.
Adding payload to the Http2Client example.

Modifications:
When trying out the Http2Client example I noticed that adding a request
payload would not cause a data frame to written. This seems to be
because writeHeaders completes the promise, and then the writeData
call ends up in FlowControlWriter.writeFrame, isDone is true and
the data released and the call aborted and returned.
Adding a new promise for the writeData method allows a data frame to be
written.

Result:
A body/payload can now be sent to the server. The example was updated to
simply echo the payload received back to the calling client.
Add WebSocket Extension handlers for client and server.
Add permessage-deflate and deflate-frame WebSocket extension
implementations.

Motivation:

Need to compress HTTP WebSocket frames payload.

Modifications:

- Move UTF8 checking of WebSocketFrames from frame decoder to and
external handler.
- Change ZlibCodecFactory in order to use ZLib implentation instead of
JDK if windowSize or memLevel is different from the default one.
- Add WebSocketServerExtensionHandler and
WebSocketClientExtensionHandler to handle WebSocket Extension headers.
- Add DeflateFrame and PermessageDeflate extension implementations.
migrate netty to FJP
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