Add examples for atomic operations to recipes (docs & code)

The zookeeper docs do a good job of explaining how to do low-level synchronization primitives with zookeeper. But it's not immediately obvious after reading the docs how to implement higher-level synchronization primitives - for example how to do zookeeper equivalents of the java Atomic concurrency primitives, like AtomicInteger.

So as per Patrick Hunt: "This is def. something we should add to the recipes (docs & code lib)"