Optionally disallow "WIP", "Merge" ( and fixup! / squash!)

[Narretz]

These exceptions are hard-coded in https://github.com/jzaefferer/commitplease/blob/cec0dd6d28ed1ec42843285192072877830c1f96/lib/validate.js as far as I can see.

This is okay when a commit range gets reviewed before merging, but to be 100% strict, you should be able to turn off any of this in specific circumstances / make it overwritable like the config)

For example, in Angular / AngularJS merge commits are actually disallowed - everything must be rebased and the merge commit must be squashed.

We are also adding commitplease to Travis in AngularJS and fixup! and squash! are okay, but WIP isn't

[jzaefferer]

@Narretz would you be interested in implementing the necessary change in a PR?

[Narretz]

Not at the moment - I'd need to familiarize with the code first

[jzaefferer]

A PR with updated tests or docs or both would already help. Otherwise I'm hoping @all3fox can help out