Release v2.0.20 - 2015-01-20

References: #195

• Feature - Aws::EMR - Added support for Custom security groups feature for
  Amazon Elastic MapReduce (EMR). Custom security groups allow you to define
  fine grain control over the security rules for your EMR cluster by specifying
  your own Amazon EC2 security groups.
• Feature - Aws::CognitoIdentity - Amazon Cognito now allows developers to save
  the association between IAM roles and an identity pool via the
  #set_identity_pool_roles API. Identity pools with IAM roles associated can
  use the new #get_credentials_for_identity API to retrieve a set of temporary
  credentials based on the associated roles. Roles associated to the pool must
  be properly configured to work with Amazon Cognito. Developers can still use
  the #get_open_id_token API in conjunction with STS
  #assume_role_with_web_identity API if there are no roles associated with
  their pool.
• Feature - Aws::AutoScaling - Added support to Aws::AutoScaling::Client for
  classic link.