Add support for sass style comment in `.scss` files

[b2l]

Comments should be in the form:

//doc
//  ---
//  title: something
//  category: ...
//  ---
//

Always have double space between the // and the content

[b2l]

@jdcantrell Do you think you can merge it in this state? I'll be happy to change some things if you prefer, but I would really appreciate if I can use upstream again.

[Epho]

+1 for this update, would love to have this merged in as well

[j1348]

+1