Use RxJS for the server, too

For the moment the server is just some hairy coffee-script,
than watch folders, compiles stuff on the fly, stream assets to the clients..

that's a complex job, and it should be done using Rx, not basic callbacks

here are some hints to use Rx on node / io.js
https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/nodejs/nodejs.md
