Improve the Javadocs

[david-at-aws]

The javadocs for the generated service and resource interfaces are pretty bare-bones at the moment. Comment here if you'd like to see this prioritized.

What information would be useful to you in the Javadocs? More information about what a particular action method does (versus just a pointer to the underlying SDK client method)? More information on the behavior of getter methods (do they make network calls or not)? Code samples? Other things I haven't even thought of?