Refactory for Reference files + Gruntfile update

I had to make a files refactory on the docs files to get only 2 files (reference.js and main.css) for the YuiDoc theme. 

The reference is as usual in: /docs/reference
The YuiDoc theme is in: /docs/yuidoc-p5-theme
The sources for the theme are in: /docs/yuidoc-p5-theme-src (here you have /sass, /scripts and /psd)

Gruntfile.js was also modified and optimised to allow automatic builds of the Reference when modifications to the sources are detected (by using `grunt watch` as usual).