fix: resolve configuration file precedence issue

[paduszyk]

The package searches its configuration in some standard config files following a strict order:

1. pyproject.toml
2. setup.cfg
3. tox.ini

That's great as enables variety of config schemes. The problem is that the searching loop is broken when it finds the file, not the actual configuration in it. So, if you want to define configuration in setup.cfg, but have other tool (e.g., black in my case) configured in pyproject.toml (or even if you define project metadata in that file, following PEP 621), docformatter does not see the desired settings.

In this PR, I propose a simple update of configuration.Configurater class constructor to resolve this issue.

[weibullguy]

There needs to be some tests for the new functionality.