[feat] Add uncenter mixin
Merge pull request #265 from joaostein/uncenterMixin

[feat] Add uncenter mixin
Add inline documentation for scss functions

- Sticking to JSDoc conventions as closely as possible
- Using $ for @param names
- Using @warn instead of @throws
- Using {list} type for Scss lists
Add innline documentation to the Scss mixin set
Add inline documentation to the Stylus mixin set
Add inline documentation to stylus

It's ported over from the scss version, but with
any irrelevant bits like non existant parameters removed.
Improve a couple of type hints