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.
Oh, LOL, wow, I apparently fail at reading.  Yeah, the annotation is supposed to be mismatched-series according to the docs.

The naming of `disjointPrev` is short for "disjoint previous" meaning the previous datum in the disjoint series.  I'm open for suggestions on name.  Will fix the annotation...