add release workflow

[nikita-b]

I moved the release workflow to a separate step, and instead of a tag trigger, I added a release trigger. We will publish a new version when we create a new release.

[codecov]

Codecov Report

Merging #156 (aee7802) into master (2b02b70) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #156   +/-   ##
=======================================
  Coverage   90.72%   90.72%           
=======================================
  Files          31       31           
  Lines        1294     1294           
=======================================
  Hits         1174     1174           
  Misses        120      120           

[nikita-b]

@jrxFive @jonathanrcross Could you, please, check this MR? I would like to do a new release in 1-2 weeks. :)

[jonathanrcross]

LGTM Thanks @nikita-b!