Add coverage as optional dev requirement.
Merge remote-tracking branch 'refs/remotes/origin/fix-travis-100' into coveralls-83
Run tests with pytest-cov to gather coverage info.
Simpler coverage gathering.
Attempt to hook up coveralls reporting.
Link to coveralls badge.
We need coverage installed.
Merge remote-tracking branch 'refs/remotes/origin/master' into coveralls-83

Conflicts:
	README.rst
Merge pull request #108 from ClusterHQ/coveralls-83

Coveralls support.

Fixes #83.