CLI Reports from XRay

[tmaiaroto]

Following up on #13 it would be nice to visualize some of the data recorded in XRay without combing through the AWS web console.

The most obvious thing here is a command to return the success/failure rates of an application's handlers along with timing information (min/max/avg execution time).

XRay has an API for getting this information, it just needs to be hooked into a command.

The hard part will be identifying all of the subsegment and annotation values. I'm not sure what the XRay API has just yet. So I don't know if there's an index of them all, or if now we need to hold a list of valid values to look for. That's going to change for each application, so it's hard. If XRay doesn't have any sort of aggregation or reporting support in its API, it may not make sense to do this.