Add null check
Add FilteredMessageBuf
Rename ChannelHandlerAdapter to ChannelDuplexHandler / Rename CombinedChannelHandler to CombinedChannelDuplexHandler with fixes / Add a new ChannelHandlerAdapter implementation
Fix missing freeOutboundBuffer impl
Revert some of the changes in CombinedChannelDuplexHandler due to design mistakes
Remove useless ChannelInbound/OutboundHandler