Creates UUIDs version 1, 3, 4, and 5 in pure ruby.
I needed a uuid generator for Ruby. There's nothing wrong with current implementations, I just wanted a simpler one, bundled in a single file (rather than a gem), that could comply with RFC4122. I found this charming one using Ruby Struct by Shyouhei Urabe (aka mput), which is not online anymore (http://raa.ruby-lang.org/project/ruby-uuid/), unfortunately. I had it in my HD, so I decided to put it back online. All the credit really goes to mput. I just added a method to set the version of UUID, since that was missing in the original code. I also intend to implement version 2, which is also missing.