Enhance nested model error tests: a) to ensure the missing key is listed in the userInfo; b) to check for errors in both arrays and dictionaries.
Propagate errors in nested models out (instead of re-generating a generic error) so that the correct error can be seen by the end-user.
Encourage invalid data errors to use more explicit messaging by requiring that a message is passed in.
Fix security issue with an error log that could allow data to be read by placing format string special characters in a class name.
Note: I think this is purely theoretical because the class name couldn't have a % in it, but it's cleaner anyway.
Merge pull request #102 from j-h-a/improve-error-messages

Improve error reporting and update tests.