* Remove lexers which have been fixed in Pygments 2.4.0. * Add Pygments >= 2.4.0 to test runner. * Fix pages that triggered lexer errors. Co-Authored-By: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>
When building the docs in a virtualenv we need to install PyYAML in addition to sphinx, otherwise the `import yaml` will fail.