#81 Add yaml schema validation

[Nicolas Hainaux]

Either from a json schema, library https://pypi.python.org/pypi/jsonschema
+ see this http://json-schema.org/documentation.html
(based on this suggestion: https://stackoverflow.com/a/22231372/3926735 and see this: https://json-schema-everywhere.github.io/yaml )
or from: https://pypi.python.org/pypi/voluptuous/