Ability to look up parameter values from EC2 Parameter Store

[joffotron]

i.e. have

{ "MyParam": "<<ssmparam: /path/to/my/parameter/>>" }

See: http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ssm-parameter.html
and
http://docs.aws.amazon.com/systems-manager/latest/userguide/sysman-paramstore-walk.html

Would have to do API calls to look up param values at the time of parameter expansion (like with KMS)

(again mainly leaving this as a note for me to implement this :p)