Issue/70 property access

[bogdanadrianmarc]

This PR addresses issue #70 by changing how property access works in sapi-client-ruby. path_first and path_all retain their original functionality, while direct property access such as calling resource methods directly (for example instead of doing path_all('jurisdictionDetail') one can do jurisdictionDetail as a method call) will return the value if that property is in the API returned JSON, nil if the property is not in the returned JSON but is in the model spec, or raise a MethodMissing exception if none of the above evaluates to true