jsdoc comments for random data function

@imlucas 
Added lots of documentation for the random data function added in #39 to fully replace `chance.randomFunc()`. 
Next step I will use `dox`, or put those function in a separate file to make reading the comments easier (a lot of scrolling is needed to read the comments for now).
Hope they can help clarify the new random functions which hopefully are more handy than directly invoking chance function.