Extract versioning from Crepe core

API versioning will be moved to [crepe-versioning](https://github.com/crepe/crepe-versioning).
This closes #56

Signed-off-by: David Celis <me@davidcel.is>
I was just noting that we didn't _need_ it anymore. I think the option to override could still be good, and it would make writing/integrating crepe-versioning a bit easier.