Add git user options

[hipstersmoothie]

What Changed

Get git user from cli args, config, or package.json.

Why

Previously auto would fail when no git user was set.

closes #34

Todo:

• Add tests
• Add docs
• Add SemVer label

[codecov]

Codecov Report

Merging #37 into master will decrease coverage by 0.05%.
The diff coverage is 76.47%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage   79.12%   79.06%   -0.06%     
==========================================
  Files          12       12              
  Lines         800      817      +17     
  Branches      104      100       -4     
==========================================
+ Hits          633      646      +13     
- Misses        150      152       +2     
- Partials       17       19       +2

Impacted Files	Coverage Δ
src/github-release.ts	94.66% <ø> (ø)	⬆️
src/cli/args.ts	100% <100%> (ø)	⬆️
src/main.ts	24.08% <66.66%> (+2.85%)	⬆️

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