Expect configurability and connection info in errors

Added

• Expose connection info in errors with the addition of Error::local_addr and Error::remote_addr. This allows you to get the local & remote addresses involved in a request, if any, even if an error occurs. (#336, #337) @sagebind
• Allow use of the Expect header to be configured via Configurable::expect_continue. (#303, #311, #340) @sagebind

Dependency Updates

• Update env_logger requirement from 0.8 to 0.9 (#330) @dependabot