aphyr/riemann — pull request #404 by blalor (2014-06-17 20:17:26+00:00)
Title: Extend changed to optionally capture previous value

Providing this information allows the child streams to know what the previous
state was, which could be used to drive notifications or corrective actions.

This is my very first bit of Clojure, and I'm still a complete Riemann neophyte.
It's entirely possible I'm on the wrong track, here, but I wanted to get some
feedback.