Uagents

Updates:
- Includes required API key in mailbox server authentication flow

New features:
- support for mailbox service
- better logging output

Features:
- Core framework with interval tasks, message, and event handlers
- Initial exchange protocol implementation
- Signed and unsigned message handlers
- Supports sync (wait for response) and async message exchange
- Interface with Almanac smart contract on Fetch.ai ledger
- Optional Tortoise-ORM integration
- 10 examples
- Initial docs and test cases