Pelican 4.0

• Replace develop_server.sh script with pelican --listen
• Improved copy/link behavior for large static files (e.g., videos)
• New {static} syntax to link to static content; content linked to by
  {static} and {attach} is automatically copied over even if not in
  STATIC_PATHS
• Pages can now have draft status
• Show current settings via new --print-settings flag
• New signals: feed_generated and page_generated_write_page
• Replace Fabric with Invoke and fabfile.py template with tasks.py
• New ARTICLE_TRANSLATION_ID and PAGE_TRANSLATION_ID settings to
  specify metadata attributes used to identify/disable translations
• HTML reader now parses multiple occurrences of metadata tags as a list
• New Blogger XML backup importer
• Wordpress importer now updates file links to point to local copies if the
  files were downloaded with --wp-attach.
• Many bug fixes, tweaks, and other enhancements