Added support for input elements to the countUp object

I have added support for input elements to the countUp object by creating a function "formatPrint" that checks if the target html element is input, and if it is, applies the animated frame or '--' for errors, to the target's value instead of innerHTML element. 

I am new to forking and javascript so please let me know if I have done anything inappropriate.

Great project. I am using it on a site I'm developing and it's been fantastically helpful.