Hype DataFill 1.2.1

Inspired by Mark Hunt from Tumult forums I added a third parameter custom callbacks!

Allowing for things like mapping data-bgcolor to the class .bgcolor and firing a custom callback when the data-bgcolor changes or is set.

HypeDataFill.mapDatasetToClass('bgcolor', '.bgcolor', function(elm, value){
	elm.style.backgroundColor=value;
});

^{Also, I modified the read me and switched to semantic versioning. Minor update to observe class changes in IDE.}