[WIP] Cycling values in CSS

WIP for #8. [Specs](https://github.com/hayaku/hayaku/wiki/Cycling-values).

TODO:

- [x] Check if the current region was in the area where the first one made changes to.
- [x] Check if the region is multiline, do nothing in that case, or?
- [x] Bug: sometimes multiple regions appear, often when at start.
- [x] See if we're at CSS scope and stuff.
- [x] Handle multiline props, when lines ending with `[,\]`, etc?
- [x] Handle selection somehow?
- [x] Refactor common things into a abstracted module.
- [x] Add cycling for numeric values.
- [x] Add fallbacks for undetected values (colors ATM etc).
- [ ] Decide on keymaps.
- [x] Bug: selects incorrect item when after the last item.