integrate `stylelint` for linting css

[Alexander Akait]

https://github.com/stylelint/stylelint

[Damon Bauer]

@evilebottnawi - thanks for the suggestion! I have not used stylelint before. I'd welcome a pull request with this feature if you want to make one.

[Austin Peterson]

+1
but make sure it supports sass/scss with or without tabs. I think I ran into trouble with tabs in .sass files. prob something I will integrate when it works for me.

https://github.com/theskillwithin/hrtcup/blob/master/package.json

[Damon Bauer]

Closed in #23. Thanks for the suggestion @evilebottnawi & @theskillwithin