Update docwriter dependencies

Update dependencies. The mkdocs-material codebase has gone through many changes and needs some manual testing to make sure everything is working as expected.

• .gitlab-ci.yml: Install apt dependencies quietly.

• .travis.yml: Add deprecation notice.

• README.md: Update links to the FreeType repository.

• docs/markdown/stylesheets/extra.css: Updated to work with changes to mkdocs-material. The max-width property for .wy-nav-content and margin-left property on .md-sidebar--secondary are removed because max-width on .md-grid is sufficient to match the page width with earlier versions.

• requirements.txt: Update package versions:

  mkdocs: 1.1 -> 1.1.2
  mkdocs-material==4.6.3 -> 7.0.7
  [SECURITY] PyYAML: 5.3.1 -> 5.4.1

• setup.py: Mark package Production/Stable

• tests/freetype.sh: Clone from Gitlab.

• tox.ini: Update Python versions.