Code refactoring in PelicanAutogenSlug
Remove redundant codes in PelicanUpdateDateCommand
Extract PelicanTools to PelicanPluginTools.py
Refinement on Pelican article detection (files newed by New Article comment are Pelican articles)
Move EventListeners to PelicanPluginEvents.py
Modify PelicanGenerateSlugCommand
Refined detect_article_type: check filename extension first
Modify PelicanInsertMetadataCommand
Removed redundant codes from PelicanPluginTools.py
Fix bug in meta_type detection