Use a Celluloid::Version class instead of a constant.

This is a WIP to fix [the trello issue Tim sent me](https://trello.com/c/Pmjk5yz7)

Is there a spec for this that I can use? I'm guessing due to its nature it may be hard to test.

Is this even remotely going to scratch the surface of fixing this issue?

I'm not convinced this does anything, but I'm interested in opening up a dialogue around this issue to understand the root cause of how you include Celluloid without requiring it.