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
- 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.
Now it is possible to know when the parser failed.

- fixed the update method of code, and now actually returns the update result to the client
- now an alert is displayed when the parser couldn't parse the source, until it can finally do it again
- enhanced code and documentation of the alert method, and made possible to disable the close button