allow zmq context as param when creating sockets.
Merge pull request #142 from mknoszlig/master

Problem: cannot use inproc transport when creating sockets.
define global context in template.
Merge branch 'master' of https://github.com/zeromq/zproto
Merge pull request #143 from jemc/master

Problem: C server needs lookup table for valid events in each state
Merge pull request #144 from mknoszlig/master

Problem: passing context from outside seems unnecessarily complex