Tooltip show/hide interaction could be clearer

[katiehockman]

"If the tooltip is invoked when the trigger element receives focus, then it is dismissed when it no longer has focus (onBlur). If the tooltip is invoked with mouseIn, then it is dismissed with on mouseOut." https://www.w3.org/TR/wai-aria-practices/#tooltip

This could be clearer to outline the following use case:

1. MouseIn on the triggering element (the tooltip is now shown)
2. Then focus on the triggering element (the tooltip is still shown)
3. Then Mouseout of the triggering element while the triggering element still has focus.

Following the authoring practices, this could be interpreted to mean that the tooltip would hide despite the fact that the triggering element has focus.
That should either be stated more explicitly or changed such that the tooltip is always visible if the triggering element has either focus or mouse hover. If changed in this way, then step 3 above would keep the tooltip open since the triggering element has focus despite the mouse out event.

[mcking65]

Related to #128