Scratch notes

- have been experimenting with a few approaches to coherence sorting
- have decided on a method using Spectrogram() class _crosspower method
- most of what is in coherence sorting now is just messy, half tested, experimental muck
- but it has a form of what I would like later, and there may be a few nuggets
- so, against my better judgement I am committing it and tagging associated with issue #119