[CloudFormation] Add waiter for stack completion
[CloudFormation] Add resources for stacks
[CloudFormation] Better populate resource attributes

Avoid n+1 redundant queries to populate stack resource attributes.

Per @trevorrowe’s comment: http://git.io/J2EFyw
[CloudFormation] Add Events resource
Merge branch 'master' into cloudformation_resources
[CloudFormation] Rename Event#event_id => Event#id
[CloudFormation] Improve resources

Per @trevorrowe’s comment: http://git.io/rx3KYg
Merge branch 'cloudformation_resources' of https://github.com/ktheory/aws-sdk-core-ruby into ktheory-cloudformation_resources

Conflicts:
	aws-sdk-core/lib/aws-sdk-core/cloudformation.rb
Removed Aws::CloudFormation waiters.

These will be added back shortly when the expanded waiter format is
added.

See #127