All version classes should be serializable

[rbellamy]

Serializable version classes with unit test

---

This change is 

[rbellamy]

@zafarkhaja my PR is not the oldest on your list, so by no means am I trying to jump ahead in line - this is just a gentle ping to find out if you have any idea when you'll have a chance to merge these outstanding PR's?

[rbellamy]

@zafarkhaja - any word at all?

[rbellamy]

Gah, this is why GitHub Organizations are so useful. Once again, another project that is essentially dead because the original author couldn't be bothered...

[zafarkhaja]

Hello Richard, I hope you're doing well!

Your frustration was valid, and I'm sorry it took me this long to get back to you.

I appreciate you taking the time and effort to contribute, however I'd prefer serialization proxy pattern to using the default serialized form. I wasn't sure if you'd be still interested to resubmit, and, anyway, wanted to speed things up to clear the backlog as soon as possible, so I went ahead and implemented the feature myself (8c22fdf).

Have a nice day,