Add FixedCompositeByteBuf which can be used to write an array of ByteBuf in an efficient way.

This implementation does not produce as much GC pressure as CompositeByteBuf and so is prefered,
for writing an array of ByteBufs. Be aware that FixedCompositeByteBuf is readonly.

When using this in a project that make heavy use of CompositeByteBuf for writes we was able to cut
down allocation to a half.
Replace usage of StringBuilder by AppendableCharSequence for performance reasons
[#2033] Correctly handle adding of IdleStateHandler after Channel was already active and registered
SockJS Protocol support for Netty 4.
Bumped version to 4.0.0.CR10-SNAPSHOT
Moving SockJSProtocolTest to protocol package
Removing log statement.
Updated to reflect recent changes in Netty API.
Updating to 4.0.4.Final-SNAPSHOT.
Releasing the discarded buffer and not simply ignoring them.
Adding instructions about how to run the sockjs-protocol tests.
Making sure that writeAndFlush is used and not simple write where
approriate.
Code clean up and document updates
Fixing the ignored jsonEncodingTestXhrServerDecodes test.
Docs and minor updates from PR feedback.
Making Frame extend ByteBufHolder and subclasses extend
DefaultByteBufHolder.
Making HtmlFileTransport extend ChannelDuplexHandler and use
ByteBufAllocator, and reduce writeAndFlush calls.
Reducing buffer copies and adding ThreadLocals for SimpleDateFormat and
MessageDigest.
Making JsonPollingTransport extends ChannelDuplexHandler and reducing
buffer copies.
Removing duplicate close.