v0.3

• Model.init = _declarative_constructor
• Support pshell scripts
• Properly handle read only mode
• Properly handle returning connection to the pool
• Format code with black
• Check that DB is upgraded to latest Alembic version
• Use py3.7 as default, drop support for py34 and py35
• Export type annotations for users
• Add circleci config
• Change license to MIT
• Remove deprecated pytest_runner