0.5.0

Added:

• AbstractFeed class which can be extended in custom feed implementations

Changed:

• Substitute laminas/laminas-feed and jdecool/jsonfeed with custom implementation
• Rename Enclosure class to Attachment
• Allow multiple attachments for JSON feeds
• Integrate FeedCategoryInterface into FeedInterface
• Integrate StyleSheetInterface into FeedInterface
• Adjust namespace for classes Attachment, Author, Category, Image