[WIP] Add warning support

[tagliala]

Close standard/snazzy#29

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update [x] Bug fix [x] New feature [ ] Other, please explain:

What changes did you make? (Give an overview)

Which issue (if any) does this pull request address?

Is there anything you'd like reviewers to focus on?