Dataclasses-jsonschema

Implemented 52 - Support the `readOnly` and `writeOnly` OpenAPI 3 keywords

Implemented 47 - Support property descriptions using field metadata
Fixed 45 - Field defaults using default_factory are included in generated schema

Fix 42 - Handle fields using `default_factory`
Fix 41 - Correctly handle fields with a default nested class instance

Fix 36 - Errors when generating json schema with default values
Fix 38 - Optional fields without None default value not handled correctly
Fix 39 - Unable to disable validation in nested dataclasses

* Fix 30 - Support default field values
* Fix 31 - Support fields excluded from __init__
* Improve README

* 13 - Implement support for type unions
* Add support for embedding into swagger 3.0 specs
* 12 - Improve type annotations on `from_dict` method
* 27 - Deprecated calling `JsonSchemaMixin.json_schema()`. Add `all_json_schems`
* Raise custom ValidationError instead of using the validation lib ValidationError