Make parser try to find declared attributes in a class, and not keys in the result

If we try to generate arguments in f(x) of the responses that AWS gives us, there can
be some suprprises, as when AWS could add an extra key to it's output, we would try
to create an object with that unknown key, rendering the SDK vulnerable to being broken
by additions by part of the server.
Merge branch 'master' of https://github.com/pplu/aws-sdk-perl