Added GPG signing of artifacts

[freemanjp]

For better repository support.

[codecov]

Codecov Report

Merging #33 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #33   +/-   ##
=========================================
  Coverage     82.39%   82.39%           
  Complexity       77       77           
=========================================
  Files            15       15           
  Lines           409      409           
  Branches         66       66           
=========================================
  Hits            337      337           
  Misses           27       27           
  Partials         45       45

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