Add OutputWriter implementation for posting metrics to Stackdriver over HTTP.  Update BaseOutputWriter to support numeric settings as well as String settings.
fix typo in log message
Update how we make the metric names, take advantage of the aliases in the config and only add the extra value key to the end if it is different than the attribute name.  Use StringBuilder for efficiency
Merge pull request #84 from Stackdriver/master

Initial version of OutputWriter for Stackdriver