Move documentation to `doc` directory

Issues #97, #134

Documentation is updated, separated into 4 files and moved to `doc` directory.
`CSSComb` and `csscomb` are all renamed to `CSScomb`.

![tumblr_me8rcipt3r1rpxgkao1_500](https://f.cloud.github.com/assets/872004/1796189/04e3a992-6a5a-11e3-84e2-202a89e384c7.gif)