Fix crash when fetching remote image fails

Fix social cards folder when directory URLs are disabled

Fix uncompliant author's email format

Integrate with Material Blog plugin

Enhance social card integration to support Material Blog plugin and m…

…inor fixes

Allow per-page description customization

Cached and robust HTTP requests

Restore compatibility with Python 3.8 and Python 3.9

Hotfix bug introduced in previous version

Add per-feed custom titles and abstracts