Option to clear styles when finished

[mattpardee]

I love Firmin, thank you so much for creating it. This is a feature request, to remove the styles set in the "style" attribute of an element after an element is done being animated.

Typically I'll animate something and then later change some position/height etc value, and it will use the same timing method and speed set previously by Firmin. If possible I'd like to include a "clearStyles" : true flag. Thanks!