load additionalProperties
additionalProperties in prim_factory

- properties should be a dict, not list
fix for additionalProperties

- we won’t make sure every properties would be shown with None,
none_count is removed. Users have to check if a property exists before
access it, or use dict.get with default.
- support additionalProperties
- do not pop input dict
add test case
add is_produced
add produce hook
AdditionalPropertiesContext
default of additionalProperties is True
Merge pull request #20 from mission-liao/addp

for additionalProperties with Schema