Fix CSS and Javascript paths

`/css/docs.css` points to `http://dryan.github.io/css/docs.css`, which does not exist. Stripping the leading slash (so we have `css/docs.css`) fixes it (-> `http://dryan.github.io/css-smart-grid/css/docs.css`). Same for `modernizr.js`.
Merge pull request #6 from mtsk/patch-1

Fix CSS and Javascript paths in layout file