4 - Upgrade to TypeScript 4 and simplify Form declarations.
5 - Add support for overlay modules:
6 - Overlay modules inherit all the forms of the parent module, but specific forms can be replaced
7 if they have changed since the prior year.
8 - TaxReturns now have `constants` property, to inject inflation-adjusted constants, which is
9 what most year-to-year changes require.
10 - Add the **fed2020** module as an overlay to **fed2019**.
11 - Add the **fed2021** module as an overlay to **fed2020**.
12 - Some common values on `Form1040` are now accessed symbolically in referencing forms, to make
13 them immune against year-to-year line number shifts.
14 - The `Line` class now supports a `LineOptions` to hold less-common options.
15 - Currently there is only a `formatType`.
16 - Add limited support for ISO options exercises to AMT/Form 6251.
19 - Add support for itemized deductions/Schedule A.
20 - Add limited support for the AMT/Form 6251.
23 - Only publish the dist/ folder.
26 - Include examples in the NPM package.