Add run on repl.it badge to README

[nraikm]

This pull request configures this repository to be run on Repl.it. It adds a .replit configuration file and a Repl.it badge to the README. You can read more about running repos on Repl.it here, or view the Repl here.

[codecov-io]

Codecov Report

Merging #117 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #117   +/-   ##
=======================================
  Coverage   92.69%   92.69%           
=======================================
  Files          31       31           
  Lines        1259     1259           
=======================================
  Hits         1167     1167           
  Misses         92       92

---

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 f439f92...6cebf87. Read the comment docs.