EMR hospitalization indicator

[capnrefsmmat]

• needs tests

[mariajahja]

@capnrefsmmat I've added a few unit tests, with the exception of the geo_map.py and the largest update_sensor::update_sensor() function (not sure the latter is good on run time, though I can spend some more time making a smaller testing dataset if needed). Let me know.

[capnrefsmmat]

@jsharpna Both this PR and #76 have synthetic data, so you should be able to start with either. I think this PR just needs review, while #76 will require us to check the changes that Maria has recently made in the covid-19 repository and port them to the new code.

Beyond those tasks, the remaining thing I wanted to do was to combine code. This repository contains _delphi_utils_python/, a Python package for common features and functions; I wanted to extract out the common features of geo_map.py to that package, so these two indicators do not have redundant code and redundant geographical data.

(The geographical stuff handles aggregation from ZIP codes to counties to metropolitan statistical areas (MSAs), states, and hospital referral regions (HRRs); it involves a bunch of mapping files we have to keep up to date and other gross stuff, so it's best that all the code shares it.)

Perhaps you could start spelunking through whichever of these two branches seems most approachable, then let us know what you think you can do and if you'd like an orientation Zoom session or anything?