Approvaltests

[Added markdown tables](https://github.com/approvals/ApprovalTests.Python/blob/main/docs/reference/markdown_table.md)

* Better support for [multiple approvals per test](https://github.com/approvals/ApprovalTests.Python/blob/main/docs/how_to/multiple_approvals_per_test.md).
* Added `verify_exception`
* [Exception utilities] (https://github.com/approvals/ApprovalTests.Python/tree/main/approvaltests/utilities/exceptions)
* Options supports `with_namer`
* Note: this breaks backwards-combability with 5.1.0 by moving `multiline_string_utils` into a new namespace (`approvals/utilities`)

You can now create `Verifiable` objects, which know how to verify themselves. See:
[Creating custom verify methods](https://github.com/approvals/ApprovalTests.Python/blob/main/docs/how_to/create_custom_verify_methods.md)
Also added `remove_indentation_from`.

* Better __init__.py for backwards compatibility
* PythonNativeReporter + PythonNative will resolve from ReporterFactory

Fixed a few pylint complaints

This is only breaking if you Extend the Namer Classes.

Breaking Changes
Namer/NamerBase
Namer is now a pure interface and the abstract parts have been moved to NamerBase
**Fix** If you are extending `approvaltests.core.Namer` you will probably want to extend `approvaltests.namer.NamerBase`

StactFrameNamer renames
* Directory -> directory
* MethodName -> method_name
* ClassName -> class_name