Add tests for error messages and improve reader IO error position

[juntyr]

* [ ] I've included my change in CHANGELOG.md

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +1.25% 🎉

Comparison is base (cc02072) 98.14% compared to head (bdcb99c) 99.40%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #497      +/-   ##
==========================================
+ Coverage   98.14%   99.40%   +1.25%     
==========================================
  Files          78       78              
  Lines       10308    10542     +234     
==========================================
+ Hits        10117    10479     +362     
+ Misses        191       63     -128     

Files Changed	Coverage Δ
src/error.rs	100.00% <100.00%> (+46.37%)	⬆️
src/options.rs	100.00% <100.00%> (ø)
tests/options.rs	100.00% <100.00%> (ø)

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