message: Fix GitHub repository status bar
diff: * text=auto
  *.cpp text
  -*.h text
  +*.h text linguist-language=C++
  *.md text
  *.csv text
  *.cmake text
  *.pc text
  *.in text
  -*.tmpl text
  +*.tmpl text linguist-language=Jinja2
  *.py text
  *.ac text
  *.am text
  +
  +tests/doctest.h -diff linguist-vendored
  +builds/autoconf/m4/ax_*.m4 -diff linguist-vendored
  