WIP: tooltip

TODO:

- [x] Test out the top-positioned tooltip some more.
- [x] Test out cases where the text is very long.
- [x] Make the background ripple from the bottom when the tooltip is appearing above the target element.
- [x] Decrease the background's animation duration for larger tooltips
- [x] Add aria role="tooltip"
- [x] Add aria-describedby to parent while the tooltip is opened
- [x] Unit tests
- [x] Proper demo
- [x] Docs
done.