Adjustments to documentation

This PR includes all adjustments to the documentation listed from

https://trello.com/c/lAGH6360/159-improve-data-model-documentation

@jh-bate @jebeck @kentquirk @nicolashery @ianjorgensen 

Please give this a once over, see if there is anything that could be explained better or just differently.  If you can think of an example that you had a question about what would happen, providing that would also be useful (I can fill in what will actually happen).
So here's what I propose for Omnipod, after reading the relevant section of the manual:
#### Target + Threshold
~~~json
    [
      { "target": 100, "correctionThreshold": 120, "start": 0 },
      { "target": 110, "correctionThreshold": 140, "start": 1800000 },
      ...
      
    ]
~~~

`correctionThreshold` is the blood glucose value below which the OmniPod bolus wizard will not suggest a correction bolus. For other pumps, this is identical either to `high` *or* `target` + `range`. Note that the OmniPod still calculates the dose to the `target`, not to the threshold. I'm not actually sure how pumps that define a range do it (although I believe they calculate the dose to the `target`, not to `target` + `range`, they just use the range to determine whether or not to suggest a dose/adjustment), but pumps that define `low` and `high` calculate the dose to bring you back to `high` if you're above it.

Another way to do this would be to redefine the `range` property as an object. So a `range` for an Animas or Tandem pump (IIRC) would be `range`: {`low`: 10, `high`: 10} and for OmniPod the `low` would always be 0 and the `high` would be `correctionThreshold` - `target`. That probably goes against the docs goals of being able to see what they can adjust on the pump though.