Enable counties from external source

[BriannaBrown-hub]

This PR adds two features to this utility.

1. By specifying external_county_data on initialization, a user can supply their own county records provided it's an array of dictionaries and each row contains statefp, countyfp, and name attributes.
2. It enables matching of county names with a . by normalizing the county name. Prior to this change St. Joseph would result in a match but St Joseph would not.