Switch to google UUID

[lkramer]

This is my attempt to address #16. I ran into a use case where I needed to use guid, and decided I'd have a go at it.

[sv]

thanks for contribution. Will have a look when i have some time. There are quite a few pending fixes/improvements that I need to push as well.
For new([16]uint8) any reason why you don't use byte here?

[lkramer]

There isn't. I will fix. (The reason is that another 3rd party library I'm integrating with stores it as [16]uint8, but [16]byte is definitely correct).

I actually notice that I made a mistake with the line in general. It should not have changed, the original was fine and will still work.

[sv]

As this will be breaking change as well, how about merging it to v1beta branch?
Also google.uuid repo saying this:
One loss due to this change is the ability to represent an invalid UUID (vs a NIL UUID).
Would it affect 0Ng coming from kdb?