Fix nested pulls

[KathrynPanger]

Issue fixed. Data can now be pulled for all sub-regions of a larger region if geography is specified correctly. Also added the ability to get all variables for a group rather than request each variable individually from the api.

[jjackson12]

Some tests aren't passing -- want to get those passing before merging. I pushed some edits to fix some basic ones, but a few things still need to be resolved:

1. We're relying on a local "config.py" file to insert the Census API key -- but without that errors pass without explanation. Ideally there's a better solution here for ensuring this is done on setup, but at least we could throw some helpful errors if that file is not present
2. "test_can_request_data" in "test_api_key.py" seems incomplete? Or I'm misunderstanding. But notably, by setting the "api_key" value as a string, it breaks the tests that come after it
3. "test_get_acs.py" is all failing because when it inserts the geography, it sets it to its enum value (e.g. "Geography.STATE" rather than that enum's string value (e.g. "state"). I'm not sure why, but I think it's happening on line 90 of get_acs.py:
   for_geography = f"&for={geography}:*"