Replace extarnal dependency on GraphicsMagick with light-weight library png-img.
For now png-img supports only node 0.10, so we should allow failures on node 0.11 for Travis
Merge pull request #73 from bem/switch.to.png-img

Replace gm with png-img
Replace codeclimate with coveralls

Codeclimate uses very outdated version of JSHint and has no intent of
updating it (I asked in May, the answer was "soon", but its October
now and its still not updated).
Amount of false positives on codeclimate now is far more then it will
be acceptable to be useful, so we are leaving it.
For coverage reports we will be using coveralls now, and for linting
`npm run lint` on Travis will suffice.
Check if file should be excluded before reading it