Tooltip positioning and on-hover target can now be distinct!

Two large changes have been made to tooltip in v0.9.0.

First, no longer do the tooltip positioning and on-hover target have to be one and the same. This change was made so you can have a tooltip show up in another location (such as following your mouse while you hover over a chart). To disconnect positioning and hover, add the follow-mouse flag. You can then pass in any coordinates into mouse-coords as an x,y array, like [x,y]. You must do the mouse calculations yourself, but the tooltip will positing itself to whatever coordinates you input. Want it to be static but away from your on-hover target? Do the same and just pass in some static window coords.

The second big change is the ability to pass in an array of targets into the "for" property, be they IDs or elements. This way, you can have one tooltip activated by multiple DOM elements instead of needing a single tooltip for each DOM element.