Cloudwatch Logs service support

This PR implements support for the Cloudwatch Logs service.

All functions for the current API version (2014/03/28) are in place and working, but full testing support is not. I will complete testing support once I fully understand how to properly test request body assertions with the included test server.

I feel like `NewEmptyQuery().AddLogGroupName(groupName)` is repeated a lot. create a utility private function perhaps ?