import US hospitalisation data

[dhan16]

We were using covidtracking's hospitalization data for the U.S. but they stopped updating it.

They suggest what to replace their data source with: https://covidtracking.com/analysis-updates/what-weve-learned-about-the-hhs-hospitalization-data. Essentially we want to get state-level data and, if we can, aggregate it to country-level.