Adds code coverage

Nearly working, the `coveralls` task is throwing an error. After `grunt test`, type `grunt coveralls`:

```sh
$ grunt coveralls
Running "coveralls:all" (coveralls) task
>> Failed to submit 'lcov.info' to coveralls: Bad response: 422 {"message":"Couldn't find a repository matching this job.","error":true}
>> Failed to submit coverage results to coveralls
Warning: Task "coveralls:all" failed. Use --force to continue.

Aborted due to warnings.
```

If someone knows how to setup coveralls in an Grunt.js environment... ?