Update ClusterConfig spec
Update e-mail in gemspec
Add a simple example

Which (unfortunately) requires the 'zk' gem (or
any other ZooKeeper gem, but I'm familiar with
'zk'). Added it as a development dependency.

Also changed version to 0.5.3, which is the same
as the one for ordasity-jars, so not really a
version bump.
Add travis config