"chosen:close" triggerable event

So... I did a thing?  In code?  And it seems to even work!

This adds a `chosen:close` triggerable event, which does the logical opposite of the `chosen:open` event.  See https://github.com/harvesthq/chosen/commit/3709cc8b8832f7a7b4558d0be97b1301b2a92b02 for the relevant code -- the other commits are for adding docs and some editor-supplied whitespace cleanup.

Fixes https://github.com/harvesthq/chosen/issues/1662

I obviously have no idea what I'm doing, so feel free to correct me.