Add an error parameter to -initWithDictionary:
Log initialization errors in MTLModel+NSCoding
Update unit tests with error handling
Add error parameters to MTLJSONAdapter
Test that an error is returned when the parse class is nil
Fix wrong error key
2x
Merge branch 'master' into better-error-reporting

Conflicts:
	Mantle/MTLModel+NSCoding.m
Merge pull request #67 from github/better-error-reporting

Allow model classes to report initialization errors