Update README:
 * Add screenshots
 * Use Mediacrush as a CDN for images to reduce load on sebsauvage.net
 * Improve page layout/sections
 * Reorder list of features
 * Add links to wiki and bug tracker
 * Add proper download links for stable/dev channels
 * Improve copyright/license notice
Merge pull request #42 from nodiscc/new-readme

Update README