Add proper support for image-url (and font-url and stylesheet-url)

[gonzalodelgado]

pyScss claims to support image-url, but doesn't really provide a way to configure the images directory the Compass image-url docs refer to:

image-url($path, $only-path, $cache-buster)
Generates a path to an asset found relative to the project's images directory.

pyScss only provides the STATIC_ROOT setting, but not the specific images_dir or images_path configuration properties present in Compass.

NOTE: this same issue happens with font-url and stylesheet-url.

[camilonova]

+1

Also will be great if you can send a path for the config.rb file

[OmeGak]

+1

[funvit]

i'm added font_root, font_url, images_root, images_url in my fork...
https://github.com/funvit/pyScss/tree/issue_114