* reworked iam_policy
* Deprecate policy_document option
* deprecate defaulting skip_duplicates to true
* No longer explicitly catch ParamValidationError.
ParamValidationErrror is already caught by ClientError
* Work with complex policy objects rather than json documents
comparisons can better cope with the special cases (eg True vs "True" )
* Enable check_mode tests and fix related 'changed' bug
* changelog
* doc cleanup based on review
