Allow concurrent, re-creatable usage

[trabetti]

Hi, I am using this package to generate uuids for a test generator. I have a use case where multiple instances of the generator run asynchronously to create tests.
I need to be able to recreate failed tests, the current implementation holds only one seed, so there is no way to ensure recreation when processes are running asynchronously.
I have forked the repository and added a UuidSource, similar to a source in math/rand, which holds the rander, this solves my use case.
I suggest to do a PR from my fork.

[pborman]

Sure, send me what you have.

[ahobson]

Any chance of a making a release with these changes?

[pborman]

Oh, sorry! I will make release 1.2 now.

[pborman]

Released as 1.1.2 (changes are too minor to be a 1.2 release). Thank you for pointing this out.