Provide default emitter for console output

Creating this to see if this can be a helpful idea for other folks.
I have an use case where I would like to be able to emit the segments via the CLI. This is to trace SSM Documents executions via XRay but can't install the XRay client on those machines. In this case, being able to use the SDK to build the segments with the proper syntax/format and just use ```aws cli``` to call ```put-trace-segment``` would be really helpful.
At the moment I'm overwriting the udp_emitter with a custom one, but would be helpful to have this as part of the SDK.