Added several enhancements for development.

These features are mainly accessible from the npm scripts feature.

Here they are:

- watch: you can now launch a watch process to rebuild your grammars anytime you change them (closes #20)
- test: launches the tests with mocha
- build: builds the package. Actually only build the grammars for now.
- stop: sends the shutdown signal to the server

Documentation has been updated accordingly.

NB: for now grammars handled by the build and watch scripts are HTML and AT. But it's easy to add others by appending them in corresponding scripts.