Updated table of supported API versions.
Corrected documentation for AWS client responses.

AWS operations documented a return object of
`Seahorse::Client::Response`.  The actual response object
is `Aws::PageableResponse` which is a subclass of
`Seahorse::Client::Response`.

Fixes #50.
Updated API models for Aws::EC2, Aws::ElastiCache, Aws::DynamoDB, Aws::OpsWorks and Aws::AutoScaling.