Support for non-linear incrementation

It would be nice to have the possibility to provide a function that maps a handle's position to a specific value, rather than using a linear function. Something like the easing functions in animations.

This comes in handy when selecting a value/range where the first half of the slider needs to represent 3/4 of the total range. For instance: a money filter, with a commonly used range of 0-3000, but with a uncommon range of 3000-6000.