assets plugin - initial commit - all tests pass

line 140?  It's to make the assets as flexible as possible.  Lets say most of your assets are in ./assets which you've set as your assets path so when you do `assets_opts[:css] = ['app']` it's going to look for `./assets/css/app.css` or `./assets/css/app.scss`.  Lets say you use components or bower, it allows you to do this `assets_opts[:css] = ['app', './bower/jquery/jquery-min.js']`.