Lightning Framework Fake Pull Request

I made this PR to myself so that Ioan/Mark can add comments inline if desired.
That's tempting, but I just read into the code and I think I'd have to allocate a lot more memory for the states (it returns a vector of all the states interpolated between two points). My implementation reuses the same interpolated state (``test``). So no reason to get ride of my version that I can see, but I'm open for convincing.