URLRewrite to set paths as absolute URL

Related to Issue #98

Example effect of this change:

`background:url(chosen-sprite.png)`
 `background:url(http://localhost/subdirectory/assets/chosen/chosen-sprite.png)`

`src: url('../font/fontawesome-webfont.eot?v=3.2.1');`
`src:url('http://localhost:8000/assets/font-awesome/font/fontawesome-webfont.eot?v=3.2.1')`