fixed: Bug where having different src and dest would cause incorrect path generation

Currently if one sets `src` and `dest` to different directories, incorrect final stylus and css locations are generated. For example, let's assume the following locations are used:

    { src: '/Project/stylesheets', dest: '/Project/public/stylesheets/generated' }

And the request path is `/stylesheets/generated/main.css`. Then the following final stylus and css locations are generated:

    source == '/Projects/stylesheets/stylesheets/generated/main.styl'
    dest == '/Projects/public/stylesheets/generated/stylesheets/generated/style.css'

These paths are obviously incorrect. I've fixed Stylus so that the paths are generated as follows:

    source == '/Projects/stylesheets/main.styl'
    dest == '/Projects/public/stylesheets/generated/style.css'