Add COVID-19 stats plugin

[examknow]

As requested at #126

[codecov]

Codecov Report

Merging #242 into master will decrease coverage by 0.13%.
The diff coverage is 22.44%.

@@            Coverage Diff             @@
##           master     #242      +/-   ##
==========================================
- Coverage   67.89%   67.76%   -0.14%     
==========================================
  Files         255      256       +1     
  Lines       16944    16993      +49     
  Branches     2068     2075       +7     
==========================================
+ Hits        11504    11515      +11     
- Misses       5227     5265      +38     
  Partials      213      213              

Impacted Files	Coverage Δ
plugins/covid.py	22.44% <22.44%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 68b57bb...471b141. Read the comment docs.