Added Coveralls.io

Refer to this blogpost: http://developer.happyr.com/coveralls-with-github-and-travis
Removed use of deprictated function

We use warning instead of warn to be PSR-3 compliant. This function will be removed in symfony/monolog-bridge: 3.0
Merge pull request #18 from Nyholm/patch-1

Added Coveralls.io
Merge pull request #21 from Nyholm/patch-2

Removed use of deprecated function
Added source path to coveralls
Merge branch 'master' into all
Merge branch 'patch-2' into all