Change basic game play to the new 0 rules
Change HTML to match the new 0 game rules
Update README.md and CONTRIBUTING.md

Mostly referring to the original files in the main [2048](https://github.com/gabrielecirulli/2048/) GitHub project.
Add Google Analytics script
Add application cache manifest
Merge branch 'zero'
Merge branch 'zero-pages'
Remove references to favicon and apple-touch icons