[feat] Tweak verbosity levels of compile error output

[slarse]

The amount of lines in compile errors are now truncated to a single line in normal output mode, default of 10 lines in verbose output and no truncation in very verbose mode.

Fix #64

[codecov]

Codecov Report

Merging #66 into master will increase coverage by 0.18%.
The diff coverage is 95.65%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
+ Coverage   93.36%   93.54%   +0.18%     
==========================================
  Files           7        7              
  Lines         392      403      +11     
  Branches       57       59       +2     
==========================================
+ Hits          366      377      +11     
  Misses         16       16              
  Partials       10       10

Impacted Files	Coverage Δ
repobee_junit4/_junit4_runner.py	90.56% <100%> (-0.18%)	⬇️
repobee_junit4/junit4.py	95.23% <100%> (+0.46%)	⬆️
repobee_junit4/_output.py	96.93% <95.23%> (-1.37%)	⬇️

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