CI and local dev improvements

[noctuid]

• Switch to github actions (current setup is not working at all due to travis website change)
• Fail build if linting fails
• Use pydocstyle, black --check, isort --check, and maybe mypy for linting
• Add Makefile for linting/testing/formatting (with black and isort) and for installing dev dependencies
• Stop using imp (pytest gives warning)
• Add makefile with test and lint commands
• Use poetry for managing dev dependencies and to publish to pypi?