Disable double dash on

[wrcYuri]

Using double-dash separator between a group and a subcommand and between subcommands can be switched off.

• fixes Double-dash separator can be used between group name and commands, has odd behavior #619

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[wrcYuri]

Hello, I've added some tests for the desired functionality, could you please take a look at those, and all the code in general.