Use new puf.csv file containing new pencon_? variables; update some logic and test results

[martinholmer]

This pull request incorporates the new puf.cps file generated by the changes in taxdata pull request 279. Those taxdata changes added two new variables (the amount contributed to defined-contribution (DC) pension plans by the taxpayer and pension contributions made by the spouse, which are named pencon_p and pencon_s, respectively). The new data variables required some revisions in payroll tax logic (because the payroll tax base includes pension contributions even thought the income tax base does not). And the pension contribution amounts are added into expanded_income causing changes in the distributional tables. Taken together, the new data and new logic cause many changes in the test results.

As a result of these data and associated logic changes, payroll tax liability is noticeably higher than before and income tax liability is essentially unchanged. So, for example, in 2018 payroll tax liability is up by $30.9 billion, which is a 2.7 percent increase, but income tax liability is unchanged when rounding to the nearest $0.1 billion.

Note that this pull request also adds the pencon_p and pencon_s variables to the CPS input data, but as of yet the values of those CPS variables are zero for each filing unit.

[codecov-io]

Codecov Report

Merging #2056 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2056      +/-   ##
==========================================
+ Coverage   99.97%   99.97%   +<.01%     
==========================================
  Files          16       16              
  Lines        3528     3530       +2     
==========================================
+ Hits         3527     3529       +2     
  Misses          1        1

Impacted Files	Coverage Δ
taxcalc/records.py	100% <100%> (ø)	⬆️

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