[#1210] Allow to use derived buffers with DefaultBufferHolder and so fix broken SpdySessionHandler
Add WebSocketFrameAggregator which takes care to aggregate fragmented websocket frames
[#1212] Fire handshake status events to notify the user about handshake states
[#1211] Fail ChannelPromise on SpdyProtocolException like it was before in 3.x
[#1202] Fix javadoc