Problem: need proper client stack

Solution: implement code generator in zproto, use to build new
zccp_client class.

Note: requires latest zproto and czmq.

To make this simple, I've ignored all complex data types in the protocol
so messages are just strings. This is fine for now.
Problem: need proper licensing

Solution: apply MPLv2 licensing to all files.
Merge pull request #6 from hintjens/master

Problem: need proper client stack