multiple improvements

- region is now a cmd-line argument
- because we can monitor the same metrics across multiple regions, the
region name is now included into the namespace prefix (via a
"{regionName}"token)
- add "overlapping points" feature : Cloudwatch's last data point is
sometimes inaccurate with aggregated metrics (by ASG or by ELB for
example), so we always "overwrite" the last 3 data points. (number of
overlapping points is customizable)
typo
remove unused attribute
improved error handling
Merge pull request #2 from Samuel29/master

Integrating Samuel's enhancements into the main repo