Add Cookbook recipe that shows how two reforms can be directly compared

[martinholmer]

This pull request resolves part of issue #1770 by adding an advanced recipe to the Cookbook of Tested Recipes for Python Programming with Tax-Calculator. The new recipes illustrates the technique for comparing two reforms without any analysis of current-law policy. It also, shows how to read reform files directly from the Tax-Calculator website using the approach discussed by @MaxGhenis in issue #1644.

The new recipe shows how to analyze the income-tax changes caused by moving from the TCJA bill as originally passed by the House (TCJA_House_Amended.json) to the TCJA conference committee bill (TCJA_Reconciliation.json).

[codecov-io]

Codecov Report

Merging #1784 into master will not change coverage.
The diff coverage is n/a.

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  Coverage     100%    100%           
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  Files          37      37           
  Lines        3028    3028           
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  Hits         3028    3028

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[MaxGhenis]

Here's a Jupyter notebook recreating this cookbook. I made a couple minor edits, like moving comments to Markdown cells and displaying the full diff_table for reference.