C19 Update With Standard Deviation Bands

I spoke too soon. Turns out that we can put standard deviation error bounds on the plot from parameter uncertainties returned by the fitting function. Plots are shown with one std dev in green.

Logistic and lognormal fits given for USA and Arkansas as these are far enough along for lognormal to be meaningful.

Let me know if you would like to see a particular country or US state, logistic or lognormal.