Move from restclient to napping

Hitherto `neoism` has used [`restclient`](https://github.com/jmcvetta/restclient) for interaction with Neo4j's REST API.  Package `restclient` has been deprecated in favor of its newer descendant [`napping`](https://github.com/jmcvetta/napping), which features a simplified API and some per-session configuration.  This will facilitate future implementation of streaming per #22.

This change should be completely transparent to users of `neoism`.  Simple benchmark testing suggests no effect on performance.  Please open an Issue immediately if you encounter any unexpected behavior.