Support for continuous integration using travis-ci

Integration with [Travis CI](https://travis-ci.org/).

Pull requests can now be merged with confidence, because `jshint` and units tests are run automatically on them. Also, a "build status" indicator on the project page shows whether the code in the master branch passes `jshint` and unit tests. CI will of course become more useful once more tests are added.

Changes:
- Added travis config file
- Added grunt task for travis
- Added npm test script used by travis
- Few README changes