Release did-0.21

[psss]

• Pass plugin configuration to koji ClientSession
• Add markdown format output to bodhi plugin
• Add markdown format output to pagure plugin
• Handle connection error fetching gitlab user
• Update instructions for the google plugin
• Add sphinx_rtd_theme to the list of extensions
• Replace deprecated calls to warn
• Fix docs building warnings, pin sphinx version
• Add support for markdown format output (Add support for markdown format output #315)
• Move line length recommendation to proper section
• Update pre-commit GH action with latest version
• Add dependency on python3-feedparser
• Replace readfp() with read_file()
• Support defining subitems for header and footer
• Give a reasonable error for unreachable wiki url
• Report Gitlab tasks-commented properly
• Fix typo in section name
• Skip own pull requests in pull-requests-reviewed