Improve line-number detection in parse errors

[timholy]

Fixes #421

[codecov]

Codecov Report

Merging #424 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #424   +/-   ##
=======================================
  Coverage   81.57%   81.57%           
=======================================
  Files          12       12           
  Lines        1536     1536           
=======================================
  Hits         1253     1253           
  Misses        283      283

Impacted Files	Coverage Δ
src/parsing.jl	93.93% <100%> (ø)	⬆️

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