Automated shapefile updates

[pdil]

Currently the process of updating shapefiles is only semi-automated. While there are scripts in the data-raw folder that will convert US Census Bureau shapefiles into data frames readable by usmapdata, it is still a process that requires manual checking of the census website and downloading the appropriate files.

In order to provide for more timely updates to shapefiles as new ones are released, it would be beneficial to create (or attempt to create) a fully automated process that can check the relevant website(s), download the files, and create the csv data files automatically.

GitHub Actions workflows can be used to facilitate this:

1. Scheduled monthly task to check US Census Bureau website for shapefile updates*
2. If update exists, download required files*
3. Process files and convert them to .csv files that are readable by usmapdata
4. Open a pull request with the changes and new files (possibly send a notification using Pushover)
5. Project maintainer(s) review the changes and ensure everything is correct, works, and tests pass
6. Changes are made manually to resolve any issues and then the pull request is merged

*Monitoring and download can be done with either shell, python, or R scripts - whichever is more ergonomic for the given task

[pdil]

PR #6 lays the groundwork for this change by modernizing the shapefiles used by the package.