Release 2.7.0

• * Add support for using chained manager method and save/delete keyword argument (gh-507)
• Added management command clean_duplicate_history to remove duplicate history entries (gh-483)
• Updated most_recent to work with excluded_fields (gh-477)
• Fixed bug that prevented self-referential foreign key from using 'self' (gh-513)
• Added ability to track custom user with explicit custom history_user_id_field (gh-511)
• Don't resolve relationships for history objects (gh-479)
• Reorganization of docs (gh-510)

* NOTE: This change was not backward compatible for users using routers to write
history tables to a separate database from their base tables. This issue is fixed in
2.7.1.