Configurable

My suggestion for how to make the program configurable.

Offences have unique IDs, which are included when reporting.
For now, you have to give the configuration file as an option, -c/--config FILE.
I've chosen YAML as the config file format.
The only config parameter now is general->disable, which takes a comma separated list of IDs as value, e.g.:
general:
  disable: C0010,C0020

Is this a good starting point?