v.1.1.6

• New AsyncConnection class that allows users to make asynchronous requests
  via asyncio.
• Add optional metadata argument to create_secure_channel_and_connect.
• Expose error status details in DmEnvRpcError exception.
• Improvements and fixes related to type hints, in particular hints relating
  to NumPy.
• Add utility functions for packing/unpacking custom request/responses.
• Remove support for Python 3.7, now that it has reached EOL.