Sanders-DeFazio reform proposal

[duncanhobbs]

This PR addresses #2237 by adding a reform file for the Sanders-DeFazio Social Security Reform Proposal.

Here is a reference for the proposed changes.

The reform has two main [tax-related] pieces:

1. Apply the combined OASDI payroll tax rate on earnings above $250,000.

2. Apply a separate 6.2 percent tax on investment income of the ACA threshold.

[codecov]

Codecov Report

Merging #2266 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2266   +/-   ##
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  Coverage     100%    100%           
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  Files          12      12           
  Lines        2995    2995           
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  Hits         2995    2995

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[martinholmer]

@duncanhobbs, thank you for your Tax-Calculator pull request #2266, which resolves issue #2237, by adding a JSON reform file for the tax-related provisions in the Sanders-DeFazio "Social Security Expansion Act" bill.

Your pull request is nicely done and I've double-checked it on my computer. I'm going to merge it into the master branch and close resolved issue #2237. Thanks again.