capepy utility to deconstruct an object path into a list of prefixes, object name, and an extension

[mehalter]

          Is it worth having a utility function in the library that deconstructs an object path into a list of prefixes (so like `pre1/pre2/obj.name` would get `[pre1, pre2]` for prefixen), and object name and an extension in one go? feels like we're doing this a bunch.

i would think we'd want it for things other than bucket notifications, hence the utility function call out as opposed to member for BucketNotificationRecord.

Originally posted by @thecaffiend in #173 (comment)

[mehalter]

This is incorrect and should be here: cape-ph/capepy#2