Tidy/ewma2

This is a completely behavior neutral tidyup and optimization of the ewma2 filter. It just tidies up mixed tab/space indenting, and removes a bunch of redundant data copying.

It should behave exactly the same as the existing ewma2 filter, but it should be a tiny bit more efficient.

Apologies for the messy merge history... suggestions on how to fix and/or avoid this in the future are welcome.