Simpler, more compact documentation template. 

Other than aesthetic changes, this PR removes `WD::Response::Element#to_html` and Bootstrap dependencies. I couldn't resist being too agressive and ended up mixing changes in the styles and the templates at the same time, sorry about that!

You can see a [sample generated doc](http://f.cl.ly/items/0W352Y2B1c011C0O2V2I/index.html).