Use cake to generate doc:site

Preview here: http://s.jiyinyiyong.info/coffee-script/index.html

Use `highlight.js` and `eco` to replace `uv` and `erb` which were previously used.
For the theme, I forked `hightlight.js`'s `tomorrow.css`, make it look like current one as much as possible.
And I have checked, the obvious links on the page are working now.
`Rakefile` is removed in `gh-pages` branch.

Related issue: https://github.com/jashkenas/coffee-script/issues/2193#issuecomment-25814876