There is no need to add the string to all event types as only Gauge
is compatible with inc/dec functionality. Removed valueStr from all
events and added a simple boolean to the Gauge event instead
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.
