Correct ASG tag types, names, and application

Ref http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_TagDescription.html.
More complete and correct LC and ASG handling

In particular:

* Add a few fields to structs to better reflect the complete AWS APIs.

* Adjust `member>` handling in XML tags to correctly parse multi-item
  elements (ref #97 for a similar case).
Merge branch 'autoscaling-improvements' of https://github.com/mmcgrana/goamz into mmcgrana-autoscaling-improvements

Conflicts:
	autoscaling/autoscaling.go
Merge branch 'mmcgrana-autoscaling-improvements'