Add option to equalize children in groups of a given size.

[jherencia]

No description provided.

[larsbo]

great job 👍

I wanted to solve the same problem using start and end values computed outside equalize() but i think this solution is much cleaner and more straightforward :-)

I also updated my children example (use bootstrap 3 + small design fixes). You can extend it with your group option if you like: http://jsfiddle.net/4QTNP/75/