We should provide a configuration format

[MarvinKlemp]

We should provide a configuration format in order to have readable commands.

The configuration should be able to:

• [ ] define which deprecations should be searched
• [ ] select an output formatter
• [ ] Add blacklisted violations #7
• [ ] If we provide rulesets online we could define different rulesets to run #4

[dereuromark]

Especially the output format (xml, json) is important for it to be used programatically.