uuid() [ refactored to produce global unique identifiers ]

Whenever I use guids/uuids I follow the form of a 8-4-4-4-12 hex number which is supposed to be practically unique each time.

http://en.wikipedia.org/wiki/Universally_unique_identifier#Definition

I think this is the 'proper' way to make a uuid. So no dependency from a seed or Date.now() or anything else.