Add support for 2023 ACS Data

[cooperjaXC]

The 2023 vintage of ACS data was recently released. So, similar to PR #139 and Issues #13, #19, #115, #124 etc., make corresponding changes to core.py and the README.rst. Add 2023 to the code tuples and set it as the default year for ACS data pulls.

[cooperjaXC]

This issue was closed with the merger of PR #151.