Include SASS / SCSS support

[cesarizu]

Is your feature request related to a problem? Please describe.
On a different version of fontawesome for ember (https://github.com/martndemus/ember-font-awesome), there's an option to add the scss files to the build. This way it's possible to include font-awesome in the sass files and use variables and other mixins to facilitate custom styling. This addon doesn't seem to include that functionality.

Describe the solution you'd like
If possible something like the other addon, a useScss: true setting that would include the files needed.

Describe alternatives you've considered
I tried looking into https://github.com/FortAwesome/font-awesome-sass but seems that it's for rails only.

Additional context
N/A