Change the structure of the config

[joshdales]

This came up in a dicussion in my PR that made me think that I'd actually got the config structure wrong, and that it wasn't actually going to be as flexible or work the way that people expected it to. So I've changed the config again:

Changes the config so that any and all keys are applicable to each option.

label:
  - any: 
    - changed-files: ['list', 'of', 'globs']
    - base-branch: ['list', 'of', 'regexps']
    - head-branch: ['list', 'of', 'regexps']
  - all:
    - changed-files: ['list', 'of', 'globs']
    - base-branch: ['list', 'of', 'regexps']
    - head-branch: ['list', 'of', 'regexps']

I have updated the readme and added more tests to cover these new cases.

[lucacome]

works as expected 🙂