Rework documentation to have a better overview of the cpp ast checkers

[97gamjak]

Fixes #129

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.62%. Comparing base (f21005a) to head (615e154).
⚠️ Report is 3 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #130   +/-   ##
=======================================
  Coverage   85.62%   85.62%           
=======================================
  Files          50       50           
  Lines        1663     1663           
=======================================
  Hits         1424     1424           
  Misses        239      239           

Flag	Coverage Δ
unittests	85.62% <ø> (ø)

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