Exploring state-by-state US COVID-19 testing data from Covidtracking.com

In case Github's Jupyter renderer is still flaky, use nbviewer to look at the file(s):

• The main file: Updated positive rate charts by state (covid_positive_rate_etc_by_state.ipynb)
• Earlier versions (covid_pos_rate_look_ny_ma_etc.ipynb)
• Much earlier versions (covid_pos_rate_compare_update.ipynb)