[feat] Prefix cli options with --junit4

[slarse]

Fix #54

This breaks backward compatibility pretty damn hard

[codecov]

Codecov Report

Merging #56 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #56   +/-   ##
=======================================
  Coverage   94.36%   94.36%           
=======================================
  Files           5        5           
  Lines         284      284           
  Branches       35       35           
=======================================
  Hits          268      268           
  Misses         10       10           
  Partials        6        6

Impacted Files	Coverage Δ
repobee_junit4/junit4.py	95.48% <ø> (ø)	⬆️

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