Refactor to use error returns

[pwr22]

Closes #69

[codecov-io]

Codecov Report

Merging #76 into master will increase coverage by 15.59%.
The diff coverage is 77.96%.

@@             Coverage Diff             @@
##           master      #76       +/-   ##
===========================================
+ Coverage   75.07%   90.67%   +15.59%     
===========================================
  Files           5        5               
  Lines         321      343       +22     
===========================================
+ Hits          241      311       +70     
+ Misses         61       26       -35     
+ Partials       19        6       -13

Impacted Files	Coverage Δ
main.go	0% <0%> (ø)	⬆️
job/job_windows.go	68.18% <0%> (ø)	⬆️
run/run.go	89.6% <100%> (ø)	⬆️
args.go	100% <100%> (+34.75%)	⬆️

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