Improving tests & colaboration

Making it easier to colaborate and test:

1. Added CONTRIBUTING.md file (automatically linked by github / default "go to" reference for contributing
2. Added `jasmine-node` as dev dependency
3. Updated Makefile accordingly (no need of installing it globally. Also, there's, no safe way of installing it globally via package.json / scripts)
4. Added `npm test` ability (standard way of testing node.js projects... Makefile is each day more unusual)