added more events, ability to unitialize

Hello Hakim. Thanks for such cool thing.

Due to problems, that meny (it's CSS transforms and other render-related things) introduces into DOM, I've written .destroy() method, that brings back original DOM state, styles and unbinds events. It's actually not so useful with touch events and threshold option, but makes meny usable on 'fat' webpages.
Also added closed and opened events for convenience. I'm using 'closed' event to destroy meny and 'opened' event for accurately producing magic after meny is triggered.