ci: implement markdownlint pre-commit hook

[redeboer]

• Removes the need to npm-install markdownlint.
• Upgrades pre-commit.
• Also did some alphabetical sorts in config files.

[codecov]

Codecov Report

Merging #178 (cc5e7dc) into master (80b87fa) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #178   +/-   ##
=======================================
  Coverage   76.25%   76.25%           
=======================================
  Files          12       12           
  Lines         598      598           
  Branches       85       85           
=======================================
  Hits          456      456           
  Misses        107      107           
  Partials       35       35           

Flag	Coverage Δ
unittests	76.25% <ø> (ø)

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