initial commit of netty4 version.
It compiles, and is more or less translated. Went back to using
channel groups because they broke my workaround and their impl
was moved to CMSv8s and should now have a substantially more
reasonable memory foot print. Probably leaking byte bufs in at
least one place; also removed the previous internal buffer pool.

Also promoted some inner classes, moved two thread extenders to
runnables, made channel state not extend a netty handler
erroneously. A lot of classes can still be simplified by actually
using netty constructs, but it's a start.