Release v1.4.0

Change Log:

• Added optional support for HTTP connections using ThirftPy2 HTTPX Client
  • thriftpy2-httpx-client was added as an optional dependency which can be installed automatically with the http extra: pip install -U aiohappybase[http]
  • To use the http client, pass client='http' to Connection
• Converted all tests to pytest from unittest/asynctest
• Explicitly declared Python 3.9 support