add docs and testing for the LoggingHandler.
Fix regression which lead to leak buffers when nothing could be read from the Channel.

This was introduced as part of #1812, but fortunatualy was not part of any release.
Optimize SslHandler

- Fixes #1905
- Call ctx.flush() only when necessary
- Improve the estimation of application and packet buffer sizes
- decode() method now tries to call unwrap() with as many SSL records as
  possible to reduce the number of events triggered
Simpler toString() for ByteBufAllocators
Don't create an EmbeddedSocketAddress every time
Improve docstrings for and of
[#1976] Fix IndexOutOfBoundsException when calling CompositeByteBuf.discardReadComponents()