Allow user to specify the @font_face src path

[kaizau]

Enables a set and forget workflow for the sass partial.

Temporary solution until I come up with a better way to manage file paths.

[fidelix]

How was this implemented?

[kaizau]

You can tweak the output location of generated files (output) and the @font_face declarations will automatically update.

Or if you're using SASS/LESS/etc, you can set an arbitrary path with preprocessor_path.

https://github.com/FontCustom/fontcustom#configuration