docs: def gen(skipdirhtml=False):
      """Generate html and dirhtml output."""
      docs_changelog = 'docs/changelog.rst'
      check_git_unchanged(docs_changelog)
      pandoc('--from=markdown', '--to=rst', '--output=' + docs_changelog, 'CHANGELOG.md')
      if not skipdirhtml:
          sphinx_build['-b', 'dirhtml', '-W', '-E', 'docs', 'docs/_build/dirhtml'] & FG
      sphinx_build['-b', 'html', '-W', '-E', 'docs', 'docs/_build/html'] & FG