Fixed Makefile for zpubsub protobuf example to use czmq_labs library.
Added some .gitignores for labs directory.
Merge pull request #718 from lovmoen/master

zpubsub protobuf example is not built using czmq_labs library.
Problem: New contributer don't know about best practices and automatic code
formatting.

Solution: Update the CONTRIBUTION.md to let them know.
Merge pull request #719 from sappo/master

Problem: New contributers don't know about best practices and automatic code formatting.
Problem: hashtagged issues aren't automatically hyperlinked in md files

Solution: hard link to issue #680
Problem: some folk seem to be hard of hearing

Solution: extend the Warnings section of CONTRIBUTING. It's sad we need
to do this yet it's clear we lose a lot of time and effort otherwise.
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.