Clean up DOM
Clean up DOM

Added onRemove function to destroy DOMElements when control is removed so they don't pollute the tree

I also changed line 24 "document.getElementsByClassName('leaflet-container')[0]" with "map._container".
Since I'm not sure why you would want to reference it externally through document when it comes in via the argument.
What if there's more than one map on the document?
What if someone just happens to have another element with the class name "leaflet-container" somewhere else on their page?
(okay, that second one is unlikely, but why take the chance?)
unbam/Leaflet.SlideMenu