Add socksx package which supports SOCKS 4/4a/5

Motivation:

SOCKS 4 and 5 are very different protocols although they share the same
name.  It is not possible to incorporate the two protocol versions into
a single package.

Modifications:

- Add a new package called 'socksx' to supercede 'socks' package.
- Add SOCKS 4/4a support to the 'socksx' package

Result:

codec-socks now supports all SOCKS versions
Overall clean-up on socksx package

- SocksV[45] -> Socks[45]
- Make encodeAsByteBuf package private with some hassle
- Split SocksMessageEncoder into Socks4MessageEncoder and
  Socks5MessageEncoder, and remove the original
- Remove lazy singleton instantiation; we don't need it.
- Remove the deprecated methods
- Fix Javadoc errors