Update and enhance docwriter
This patch series:
- Updates the FreeType version in docwriter's README.md.
- Updates docwriter's build-dependencies (Fixes #79 (closed)).
- Allows use of mistune 0.8.4 or v2.
- Sets a default output_dir to avoid a TypeError.
- Creates output_dir if it doesn't exist, so other directories can be used.
- Specifies a site_url, so
mkdocs
creates a proper sitemap.