'popper' isn't an aria role

[scottaohara]

seems that as a default this should be role=tooltip. 'popper' isn't a valid aria role, and thus it will be ignored by assistive technologies.

additionally, the tooltip should be associated with the element to which is provides this additional information by default. The demo page, for example, would benefit from having aria-describedby point to each of the example tooltips from the element they describe. This would provide better initial guidance to developers on how to use this component in a way that will be exposed to assistive technologies.