Added documentation for :version-id-marker option to list-versions
Wrap setMaxResults in maybe-int for REPL ease.
Merge pull request #39 from sw1nn/max-results-maybe-int

Wrap setMaxResults in maybe-int for REPL ease.
Merge pull request #38 from sf105/master

Added documentation for :version-id-marker option to list-versions
Copy important warning from aws javadocs.