Update .gitignore.

[eirrgang]

Ignore some common IDE project metadata.

[codecov[bot]]

Codecov Report

Merging #134 (9746106) into master (d52e1e5) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #134   +/-   ##
=======================================
  Coverage   61.53%   61.53%           
=======================================
  Files          12       12           
  Lines          78       78           
=======================================
  Hits           48       48           
  Misses         30       30           

Flag	Coverage Δ
unittests	61.53% <ø> (ø)

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