Add "OnDirExists" option

[otiai10]

Fix #30

[codecov-io]

Codecov Report

Merging #37 (54e42c0) into main (745c200) will increase coverage by 3.40%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   80.37%   83.78%   +3.40%     
==========================================
  Files           5        4       -1     
  Lines         107      111       +4     
==========================================
+ Hits           86       93       +7     
+ Misses         13        9       -4     
- Partials        8        9       +1     

Impacted Files	Coverage Δ
options.go	100.00% <ø> (ø)
copy.go	80.43% <83.33%> (-0.29%)	⬇️
stat_times_windows.go

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