Problem: creating sockets still needs multiple calls

Solution (experimental): single constructor to create socket of given
type, and bind/connect to zero or more endpoints.
Generated documentation
Generated documentation
Generated documentation
Generated documentation
Generated documentation
Updated man pages
Problem: caller needs to get new gossip tuples

Solution: send these up the pipe as DELIVER replies. Note that all
other replies up the pipe are also now formatted as NAME + args.
Problem: swarm completion test is too complex

Solution: simply count expected DELIVER messages until all received
or timed-out.
Allow default direction for attach string
Problem: need zpoller_remove for managing poller
Merge pull request #562 from hintjens/master

Problem: creating sockets still needs multiple calls