2020: ZIP code requests fail with "Unsupported geography hierarchy"

[jcgiuffrida]

Importing 2020 ACS data and having issues related to PR #105. (I modified my package to enable the year 2020 but made no other changes, so this is an FYI for bringing the package up to date to support 2020.)

The Census appears to have changed the ZIP code hierarchy. See geography level 860 in the 2019 and 2020 supported geographies documentation. In 2020, ZIP codes were brought out from under states and made into their own national hierarchy. As a result, zipcode() is now the proper method to use for 2020 data, not state_zipcode which returns an error.

As an aside, this change is probably good because a number of ZIP codes cross state lines, there's no requirement that they stay within one state apiece.

Probably this can be fixed by re-enabling the zipcode method as it was before #105 with @supported_years(2020).

[hancush]

Believe this was addressed in #117, will circle back here to confirm when we cut a release.