Add type alias for accessing Versioned enum

[jam1garner]

I believe it would be desirable to provide an alias such as:

pub type AnyVersion<T> = <T as obake::Versioned>::Versioned;

reasoning:

• less eye-sore
• "reads" better, making it easier for new users to understand
• removes redundancy of typing out "Versioned" twice, which honestly took me all of 5 minutes to get sick of :P

Willing to PR such a change but didn't want to so without first seeing if it's desirable. Name is just the first thing I thought of and ultimately not important if you have one in mind.

[doctorn]

Absolutely great idea, just added with my most recent commit. Will merge your PR and then publish a new version.