Adding UUID Interceptor

[Venkatesh S R <so...@gmail.com>]

I have added a UUID Interceptor in our agent, for generating and adding a
UUID (Type 4) in the header for every event. This is helpful for us to
de-dupe messages subsequently.

I thought it might be helpful for other as well and would be nice to add
this upstream. Thoughts?

If it helps, I can package it with unit testcases and submit a patch.

Thanks
Venkatesh