add_jurisdiction_fips: Merge FIPS codes from EAVS
In MEDSL/medslcleaner: A MEDSL Package for Cleaning Election Returns

Merge FIPS codes from EAVS

1	add_jurisdiction_fips(.data, state_postal, add_key = TRUE, must_work = TRUE)

`.data`	A table of returns.
`state_postal`	State postal abbreviation.
`add_key`	If `TRUE`, add a merge key called `merge_name` to `.data` with a call to `jurisdiction_merge_name()`. If `FALSE`, expect the merge key to exist in `.data.` already.
`must_work`	Whether adding jurisdiction identifiers must be completely successful. If `TRUE`, assert there are no `NA` values in `jurisdiction_fips`.