Tests and linting cleanup:
* migrated to pytest
* added flake8 linting
* replaced travis with github actions
* fixed pending updates bad response https://github.com/vtemian/buffpy/pull/20 (fernand0)
* replaced string formatting style https://github.com/vtemian/buffpy/pull/19 (fernand0)
* added geolocation support https://github.com/vtemian/buffpy/pull/22 (ishandutta2007)