Add proof of concept for flowalert package and command line scripts

@frengers : here's a start at converting the scripts into a python package with command line scripts.

If you pull these changes locally, you should be able to test by:

# create python virtual environment
poetry install

# configure api token
export MESOWEST_API_TOKEN=...

# try out the commands described in src/flowalert/__init__.py
poetry run mesowest-pull auxiliary_files/mesowest_pull_stations.csv > mesowest-stations.json
poetry run update-fire-data auxiliary_files/all_stations_by_fire.json mesowest-stations.json

# also checkout the auto-generated command line usage
poetry run mesowest-pull --help
poetry run update-fire-data --help