Updates to the ingestion API to align with current version of docs

PR for doc changes is

https://github.com/tidepool-org/tidepool-org.github.io/pull/22

These updates add tests and bring things in line with that PR.  Technically speaking, this shouldn't be merged until that is merged.

@jh-bate @kentquirk Please both give this a once over.  I'm not gonna want to merge until I've gotten a sign off from both of you.
I don't understand why you've called this "disjointPrev".