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 noticed that because we're extracting this, `crepe-versioning` overrides the entire mount method. Maybe there's a way we can allow conditions to be passed in to `#mount` so that we can override and call super instead?