On both macOS and Linux `python` is not symlinked to `python3` by default. To avoid confusion, we should update our documentation that instructs users to run scripts with `python` to use `python3` instead.
Having the test directory match the module we are testing means we can have scripts in the top level of utils/build_swift which can also have tests. As part of this re-structure the test utilties have been simplified somewhat and all tests no longer use a custom TestCase, rather the standard one exposed by the unittest module.
* Implemented a wrapper module around the standard argparse package, exposing the same interface with some extras on top, including a new builder type with expressive DSL for constructing complex argument parsers.
* Fixed imports in build_swift/argparse/__init__.py to make flake8 happy.
* More re-formmating to meet the exacting standards of the python_lint script.
* Added doc-strings to all the modules in the build_swift argparse overlay.
* Implemented a new BoolType for the argparse module which handles boolean-like values and replaces the hard-coded boolean values in the _ToggleAction class.
* Fixed the mess of imports in the tests sub-package to favor relative imports, so now the unit-tests will actually run as expected. The README has also been updated with a better command for executing the unit-test suite.
* Updated the add_positional method on the ArgumentParser builder class to only take a single action or default to the store action.
* Cleaned up the set_defaults method.
* Added validation test to run the build_swift unit-tests.
* Updated validation-test for the build_swift unit-test suite to use %utils.
* Fixed hard-coded default values in the expected_options module used for generating argument parser tests.
* Updated the comment in the Python validation test to run the build_swift unit-tests.
* Implemented a (mostly) comprehensive test suite for the argument parser (ab)using metaclasses to dynamically generate unit-tests for each valid argument and preset.
* Fixed failing defaults test for build_ninja.
* Added new HelpOption and IgnoreOption classes for generating tests.
* Converted default value test into individual generated tests which should give better output in case the default tests fail.
