Approvaltests

* 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

verify_best_covering_pairs `
works the same as
`verify_all_combinations`
but with a much small set in some cases:
[Table of reduction](https://github.com/approvals/ApprovalTests.Java/blob/7fa4d7b694c5e59d8949739b82b348ff3993f9d6/approvaltests/docs/Features.md#combinationapprovalsverifybestcoveringpairs)

This release add the [allpairspy](https://pypi.org/project/allpairspy/) dependency

Breaking Features
* verify_file() will now scrub it if a scrubber is attached.
**Note:** If you scrub an existing file, it will be written as UTF8, instead of it's existing encoding
* Removed Deprecated method verify_file_with_encoding(),
**NOTE:** if you call verify_file() instead, your code will work as before

You can now inject a custom comparator to check if two files are equivalent.
Minor bug fix: delete_approve file will not explode if the file does not exist.
Minor bug fix: options are passed down the stack where they were not previously being used.