added HTML5 Mutation Observe

On content change, parent and all it's child nodes (DOM node insert/remove, CSS change ex. display show/none height/width etc, HTML attribute change ex data-state) recalculate size. Support IE11+, Chrome, FF, Safari, Opera.

source: https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver
caniuse: http://caniuse.com/#search=mutation

Works for me ;)