zpubsub implemented, with examples and doc
Added zpubsub_option class; using options in zpubsub.
Merge branch 'zpubsub'

Finished work on the zpubsub class, with corresponding zpubsub_option
static companion class.
Added check for broadcast interface in zpubsub_test, skipping system test
if no broadcast interface is available.
Merge pull request #670 from lovmoen/master

zpubsub class