Fix mishandling of file paths, affecting Windows

[dolmen]

Fix mishandling of file paths, which broke running on Windows.

Issue was raised long ago by @mukexa in #5, but this is a more complete fix.

Closes #5.

[sonarqubecloud]

Quality Gate failed

Failed conditions
40.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.90%. Comparing base (1558239) to head (3e9d45c).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
resolvepath.go	46.66%	8 Missing ⚠️
io.go	0.00%	1 Missing ⚠️
refs.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
- Coverage   65.29%   64.90%   -0.39%     
==========================================
  Files           6        6              
  Lines         703      718      +15     
==========================================
+ Hits          459      466       +7     
- Misses        243      251       +8     
  Partials        1        1              

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