UUID Generation

Hello.

I have created a class that utilizes the RNG capabilities of PasswordLib in order to generate version 4 UUIDs.

I am sending you this "pull request" just to make that addition available for merging in your project. This implementation is by no means the work of a security expert. I created it for a project of mine.

If you could find the time to fine-tune it or even add another implementation altogether I would be glad to use it in my PHP projects.

However, I feel that this could be a nice addition to the already very capable PasswordLib.