Fix interactions with `*_path` and `*_dir` configuration options
Fix interactions with `*_path` and `*_dir` configuration options

Allows the usage of `sass_dir` and `css_dir` as you would expect. For
jekyll-compass `sass_dir` is relative to the Jekyll root, `css_dir` is
relative to the output root.

Fixes #9

mscharley/jekyll-compass