v1.4.0: Making release for most packages. (#4296)

Implementation Changes

• Remove deepcopy of Client._http in background transport (#3954)

Documentation

• Added link to "Python Development Environment Setup Guide" in
  project README (#4187, h/t to @michaelawyu)

Dependencies

• Upgrading to google-cloud-core >= 0.28.0 and adding dependency
  on google-api-core (#4221, #4280)
• Deferring to google-api-core for grpcio and
  googleapis-common-protosdependencies (#4096, #4098)

PyPI: https://pypi.org/project/google-cloud-logging/1.4.0/