Problem: need a command line listener

Solution: zccp_sh with one argument is a listener.
Problem: need commands for request/reply

Solution: redesign content carrying comments; use publish and
direct to send to many and one, and use deliver to send to the
end client. Add sender id, and message address. Switch content
to using msg type, as in Zyre, so we can carry multipart ZeroMQ
messages. Finally, add dictionary 'headers' field to several
commands for extensibility.
Problem: client API does not match changes in 0d5345d

Solution: add sender, address, headers and content to _zccp_client_t and
fix all related functions to use the new scheme.
Merge pull request #1 from vyskocilm/master

Problem: client API does not match changes in 0d5345d
Merge pull request #3 from hintjens/master

Problem: need a command line listener