Add citizen counts

[MaxGhenis]

Following up on PSLmodels/C-TAM#74 to add citizenship indicators, where @Amy-Xu said:

I think this issue should be closed here and re-open in taxdata.

@MattHJensen said there that:

The user I am helping wants to limit UBI eligibility to citizens.

This is a feature of presidential candidate Andrew Yang's Freedom Dividend.

One option is separate counts like citizens_u18, citizens_18_20 and citizens_21 to correspond to UBI variables. Another is simply citizens to save space, with which the analyst could approximate adult citizens as citizens * (n1820 + n21) / XTOT.

[Amy-Xu]

@MaxGhenis Thanks for following up on this issue. I roughly remember no one opens up the issue in taxdata because there were some glitches in the CPS scripts, but I couldn't recall what exactly they were.

@andersonfrailey Do you remember what happened with this citizenship indicator?

[andersonfrailey]

@Amy-Xu the current problem with the CPS scripts is that AEI has let their SAS subscription expire so we can't run them to add new variables.