Slim project has moved

The new url is https://github.com/slim-template/slim
Merge pull request #229 from PierreRambaud/patch-1

Slim project has moved
add note about history cleaning
bump rails version to 4.1.8
add command for truncate history
use depth parameter for git clone
Merge pull request #231 from fs/node-about-history

add note about history cleaning
introduce 'core' part of new CSS structure
introduces 'modules' part of new CSS structure
mark foundation-icons as vendor library
get rid of useless compass
clean up README: correct headers, wordsmith project description