Cross-aws-account-iam-role

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**Minor Improvements**

- By default the ``validate()`` method will mask AWS account id and IAM principal ARN.

**Bugfixes**

- Fix a bug that the masked aws account id doesn't looks right.

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**Features and Improvements**

- First release
- Add the following public API:
- ``cross_aws_account_iam_role.api.IamRootArn``
- ``cross_aws_account_iam_role.api.IamUserArn``
- ``cross_aws_account_iam_role.api.IamRoleArn``
- ``cross_aws_account_iam_role.api.T_GRANTEE_ARN``
- ``cross_aws_account_iam_role.api.Grantee``
- ``cross_aws_account_iam_role.api.Owner``
- ``cross_aws_account_iam_role.api.deploy``
- ``cross_aws_account_iam_role.api.mask_aws_account_id``
- ``cross_aws_account_iam_role.api.mask_iam_principal_arn``
- ``cross_aws_account_iam_role.api.get_account_info``
- ``cross_aws_account_iam_role.api.print_account_info``
- ``cross_aws_account_iam_role.api.validate``
- ``cross_aws_account_iam_role.api.delete``