Add ability to customize variables included in --dump and --sqldb output

[martinholmer]

This pull request adds to the Tax-Calculator CLI tc an option for specifying a partial dump. After this pull request is merged, if the tcdumpvars file exists (in the directory where tc writes output files), the --dump and --sqldb output files contain only the variables listed in the tcdumpvars file (plus RECID and FLPDYR, if they aren't in the tcdumpvars file). If the tcdumpvars file does not exist, the --dump and --sqldb output files contain all input and calculated variables, just as before this pull request.

[codecov-io]

Codecov Report

Merging #1735 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1735   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          37      37           
  Lines        2962    2984   +22     
======================================
+ Hits         2962    2984   +22

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

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[martinholmer]

Using this new feature, we have the following results:

iMac2:tax-calculator mrh$ date ; tc cps.csv 2018 --dump ; date
Fri Dec  8 19:22:40 EST 2017
You loaded data for 2014.
Tax-Calculator startup automatically extrapolated your data to 2018.
Fri Dec  8 19:25:24 EST 2017

iMac2:tax-calculator mrh$ ls -l cps-18*
-rw-r--r--  1 mrh  staff        205 Dec  8 19:25 cps-18-#-#-doc.text
-rw-r--r--  1 mrh  staff  448202197 Dec  8 19:25 cps-18-#-#.csv

iMac2:tax-calculator mrh$ cp tcdumpvarsX tcdumpvars

iMac2:tax-calculator mrh$ cat tcdumpvars


RECID;MARS,iitax|combined
payrolltax


c00100

iMac2:tax-calculator mrh$ date ; tc cps.csv 2018 --dump ; date
Fri Dec  8 19:29:46 EST 2017
You loaded data for 2014.
Tax-Calculator startup automatically extrapolated your data to 2018.
Fri Dec  8 19:30:27 EST 2017

iMac2:tax-calculator mrh$ ls -l cps-18*
-rw-r--r--  1 mrh  staff        205 Dec  8 19:30 cps-18-#-#-doc.text
-rw-r--r--  1 mrh  staff   21145387 Dec  8 19:30 cps-18-#-#.csv

iMac2:tax-calculator mrh$ head -2 cps-18-#-#.csv
FLPDYR,MARS,RECID,c00100,combined,iitax,payrolltax
2018,2,1,50499.58,10243.74,2518.76,7724.98

Here is a summary of those results:

                   FULL DUMP     PARTIAL DUMP
runtime(secs):       164            41
outsize(MB):         427             2

Obviously, adding more variables to the tcdumpvars file will increase the partial dump runtime and output file size.