fix mouse hovering

Hi, 

@camart commit b96e433e seems to break the mouse hovering. Try the first example on http://loudev.com/#demos. Hover the mouse onto 'elem1' on the right side, then select a few elements on the left, you'll find you can't hover on all newly appeared elements on the right.

Event delegation seems to be a good solution to #101. Please try http://jsfiddle.net/cntoplolicon/Jjx9G/ which uses the fixed code, compared with http://jsfiddle.net/cntoplolicon/3ep4y/ which uses commit a835773 right before b96e433e and has performance issues.