Make it work in Windows and macOS

[tkf]

Commit Message

Make it work in Windows and macOS (#8)

Run CI on Windows and macOS and fix bugs.

[codecov]

Codecov Report

Merging #8 into master will increase coverage by 1.95%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   81.72%   83.67%   +1.95%     
==========================================
  Files           3        3              
  Lines          93       98       +5     
==========================================
+ Hits           76       82       +6     
+ Misses         17       16       -1     

Flag	Coverage Δ
#unittests	83.67% <83.33%> (+1.95%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/core.jl	85.36% <83.33%> (+2.24%)	⬆️

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