RFR: Support yaml metadata for actions and rules

* Add: Yaml support for actions and rules meta. Both yaml and yml extensions
are supported.
* Add: yaml, yml and json meta for sample action in fixtures for testing.
I don't think so. I grepped through pyyaml code and didn't find ParseError. 
https://gist.github.com/lakshmi-kannan/2fc1eb64c696ee4f01c2