Expose Custom WiggleRate

[mergesort]

Hi there, back again with another Pow request. 😄

I'm currently trying to create a wiggle animation that is somewhere between AnyChangeEffect.WiggleRate.default and AnyChangeEffect.WiggleRate.fast. I don't really know what the ideal wiggle looks like so I was hoping to experiment a bit, but I think at the moment I'm stuck with these two choices. Is there any chance more options could be available, or having the wiggle parameters be exposed directly?

[mergesort]

Closing this out as it was merged in via #62.