Debounce and throttle event handlers

[evoyy]

This should help improve performance. I don't mind if you accept or not, but I like to use it in my fork.

[souhe]

I need to think about this change because I've never used debounce nor throttle. Is it really improves scrollbar performance?

[ingro]

Well instead of updating the state at every tick it triggers the change event only a defined number of ms, so it could be better performance-wise but could be less fluid I guess, it is worth a test in my opinion.