1.9.4 (2017-06-04)

• Fix typo in S3_Bucket.py example (#696)
• Added .Ref & .GetAtt helper methods (#697)
• Add Pseudo Parameter Ref objects (#698)
• Fix NamespaceType typo in codebuild::Artifacts() (fixes #701)
• Add IpAddressType property to elbv2. (#703)
• Add new AWS::Lambda::Function Tags support (#705)
• Added ECS PlacementConstraints, PlacementStrategy, and ServiceName (#706)
• Add missing CidrIpv6 property to securityrule. (#710)
• Add missing properties to various objects in ec2.py (#711)
• logs.LogGroup#RetentionInDays is strictly defined list (#712)
• Add ManagedPolicyName to AWS::IAM::ManagedPolicy (Fixes #714)
• Add better validations for Parameter Default types (Fixes #717)
• Add AWS::Cognito (fixes #720)
• Add required attribute, JobFlowId, to EMR::InstanceGroupConfig (#722)
• Add WAFRegional support (#723)
• fix for ElastiCacheRedis.py example to use awacs (#725)
• Add EMR autoscaling (#729)
• Add SshUsername to AWS::OpsWorks::UserProfile
• Add PlacementConstraints to AWS::ECS::TaskDefinition
• Add MaximumExecutionFrequency to Config SourceDetails