Rewrite cql-rb example without private APIs

Ione::CompletableFuture is an internal class and not part of the public API. The correct way of making this bridge is to use promises.
Remove the async code from the cql-rb example

#close didn’t work, and for the rest of them the async is just unnecessary overhead. The public cql-rb API is synchronous.
Merge pull request #4 from iconara/fix-cql-rb-example

Fix cql-rb example