Instead now we will send a warning message to the logs
and continue on with our day.
Also a guard has been added when we detect a channel has been
closed and the `Exporter.Listen` function will return out of
its loop vs always running. When a channel is closed there will
be no more data to consume, so this seems correct. It also allows
for a test to be written for the panic.
Datadog's format extensions allow attaching labels and tags to statsd
metrics, and are documented at
http://docs.datadoghq.com/guides/dogstatsd/#datagram-format
Additionally changes compare method in tests to reflect.DeepEqual, as
the tag maps don't sort deterministically, corrects an inversion in
displaying test failure cases, and treats an invalid sample value as 1
instead of throwing out the sample.
