Feat: options.closeOnClickOutside to close tooltip on click outside

[piglovesyou]

Fixes #300

[piglovesyou]

I used mousedown of capture event phase, after the fashion of Google Closure Library, that I'm sort of a believer of ;)

It's ready to be reviewed.

[FezVrasta]

Thanks!

[atomiks]

Doesn't this have a problem of creating a new document event listener for every single tooltip?

(In tippy there is a single global click listener that handles all clicks).

[piglovesyou]

@atomiks Yes, you're right. To be more modest, it can addEventListener only on the tooltip gets opened and removeEventListener when it disappears, I guess.

[httnn]

could we get a release with this?