Merge pull request #720 from hintjens/master

Problem: some folk seem to be hard of hearing
Problem: README doesn't refer to contributer guidelines

Solution: Refer to the guidelines in the README at section Hints for contributers
Merge pull request #721 from sappo/master

Problem: README doesn't refer to contributer guidelines
Whitespace
Merge pull request #722 from evoskuil/master

Extraneous white-space in VS project files.
Don't require czmq to be installed for labs
Fix and run labs test suite
Enable labs for travis
Check for pkg-config before using it
Allow NULL contexts in zbeacon_new again.

zbeacon_new had the option to pass NULL as context (it is even in the
docs). This option was lost in the transition from zbeacon to
zbeacon_v2. This commit restores this option.
Merge pull request #725 from Q-Leap-Networks/pull-labs-autotest

Fix test suite for labs and enable labs in travis builds
Problem: Labs tests shouldn't be enabled in travis

The labs contain code that is unstable hence causing a lot of errors.
But that's ok as the labs area has been create to mature unstable code.
Error in the labs shouldn't bother the main czmq project.

Solution: Remove labs testing from travis build.
Merge pull request #727 from sappo/master

Problem: Labs tests shouldn't be enabled in travis
Merge pull request #726 from ahhentz/bugfix

Allow NULL contexts in zbeacon_new again.
zpubsub: added one last example using a zproto-based test message.
Merge pull request #728 from lovmoen/master

zpubsub: added one last example using a zproto-based test message.
Problem: getting a serialized integer from a zmsg is painful

Solution: add a simple decoder (zmsg_popint).
Problem: main README is badly formatted

There are numerous small issues in the source code (like blank line
at start of source) and the mkman script that cause the README.md
to be badly formatted.

Solution: fix these.