Added params to NewRelic call

I needed support for showing request parameters in NewRelic for our API which is built with grape, so I've built it in.

![params](https://f.cloud.github.com/assets/523019/488174/97ffb354-b977-11e2-897b-60b24823b2fa.png)

I hope you can add this to your gem and release it, so we can continue using this gem.

[1]: https://github.com/newrelic/rpm/blob/master/lib/new_relic/agent/instrumentation/controller_instrumentation.rb#L273