Changes prompted by pre-merge discussion of pull request 1711

[martinholmer]

The discussion of merged pull-request #1711 and of the unrelated pending pull request #1715 have revealed the need for a few documentation changes and simplification of the logic in test_puf_var_stats.py that generates variable means and correlation coefficients from the puf.csv file.

With respect to the documentation changes in the Contributor Guide, see the discussion in #1711 and issue #1772. Any corrections in or suggestions about those changes in contributor_guide.rst are welcome.

The test_puf_var_stats.py code has been changed to drop statistics on the agi_bin variable and to reduce the numeric precision of the means (from the nearest one-tenth of a cent to the nearest dollar) and of the correlation coefficients (from three decimal places to two decimal places). These changes implement some of the ideas suggested in this comment in the discussion of pull request #1715.

[codecov-io]

Codecov Report

Merging #1773 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1773   +/-   ##
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  Coverage     100%    100%           
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  Files          37      37           
  Lines        3027    3027           
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  Hits         3027    3027

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