Various little improvements before moving to HTML edition.

- This is common practice on GitHub to always add a RADME file formatted in markdown in order to give everyone a quick overview of the project.

- Sitemap is always useful.

- Lossless compression for PNG assets is a bless (before sprites or data-uri images).

![capture decran 2014-03-25 a 00 57 08](https://f.cloud.github.com/assets/877585/2506987/6385af7c-b3b1-11e3-8466-16ae69adbe27.PNG)