Code Modernization and Type Hinting

[bmos]

General modernization, since the package was originally built to be compatible with python 2.

The major benefit here is the type hinting, especially in reference to the string literals.
With this sort of type hinting in place, most IDEs will highlight code issues before the user even runs it. It's a big improvement to ease of use.

A couple of the other improvements that are worth noting:

• All caught Exceptions are limited to specific exceptions
• Most (all?) keyword arguments are now listed explicitly so that IDEs can make them known to users
• All captured and modified exceptions now raise from, which makes error messages more helpful
• addressbatch no longer closes file-like (already open) objects, only files that it opens
• addressbatch now accepts Path objects too, not just str paths