Output to Amazon CloudWatch

Adding a new output module for Amazon CloudWatch. This allows jmxtrans
to output values into Amazon CloudWatch 'custom metrics'. See
http://aws.amazon.com/cloudwatch/ and
http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/publis
hingMetrics.html

Original code by Sascha Moellering, https://github.com/saschamoellering