Added

• Implement Clone for WeakRecipient. #518
• Implement From<Recipient> for WeakRecipient. #518
• Add Recipient::downgrade method for obtaining a WeakRecipient. #518
• Extend Sender trait with a downgrade method. #518

Changed

• Make WeakSender trait public rather than crate-public. #518
• Updated tokio-util dependency to 0.7. #???
• Updated minimum supported Rust version to 1.49.

Removed

• Remove Resolver actor. #451