Different ways of representing UUIDs

[sondr3]

Thanks for the project, I was wondering if you'd consider adding different formats of representation for the UUIDs (similar to uniq with format: :slug)? I have hacked around it myself but would prefer if it was natively supported on the Ecto type itself.

[martinthenth]

Hi! Thanks for the suggestion. I don't have a use-case for it myself but feel free to submit a PR. I looked at uniq's implementation and if it's just Base64.encode/1 then the implementation looks straightforward to me.