Add formatted tooltip text

[jaycincotta]

Specifying typeOfWidget is insufficient. For example, I'm using this with election software and would like tooltips such as:

John Smith received an average rating of 4.5 stars among 1000 voters

In addition, the current implementation of titleText makes an assumption that typeOfWidget is a noun that can be pluralized by adding an 's'. This won't work in all cases. For example, the plural of "Cherry" is "Cherries"

The tooltip needs to be calculated dynamically. I suggest adding a new property that accepts a function:

tooltipFormater: is passed the current star rating and returns a string.

[fabinca]

I'll work on this