Per capita, for each metric

[kylegrover]

Since we're comparing countries of vastly different sizes, per capita figures can be much more informative. By pulling the population data from the UN or elsewhere we could provide:

• confirmed per capita per country
• recovered per capita per country
• deaths per capita per country
• and perhaps active cases per capita per country

[kylegrover]

oops this might be a duplicate of #23

[trekhleb]

Closing this one in favour of https://github.com/trekhleb/covid-19/issues/23