Initial documentation of the intended input data-model

This is a PR with an initial proposal for Tidepool's intended input data-model.  

I believe it covers all of our current use cases for the data and should hopefully be flexible enough for us to make changes and additions as we continue forward.

For comments.  If you have a comment about a specific area, please go to the "Files Changed" view and make your comment by clicking on the line in question and writing your comment there.

If you have a high level comment, you can leave it on the top of the PR.  If you want to rewrite something or do anything more meaty, please branch off of this branch and create a PR of your rewrite against this branch.

Note: I didn't do any of the preamble required for jekyll to make these things actually render as good html.  Once we get some semblance of sign-off on content, I'll look into making jekyll happy.