René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Support of recursive and circular references","articleBody":"**Is your feature request related to a problem? Please describe.**\r\nReferences to schemas that have not been processed yet are not supported now. See the example.\r\n\r\n**Describe the solution you'd like**\r\n I suggest to add models that are referenced without properties. And fill in the properties later. This adds the ability to refer to schemas that have not been processed yet.\r\n\r\n**Describe alternatives you've considered**\r\nAlso it may also be easier to create all models without properties first, then add properties with second pass.\r\n\r\n**Additional context**\r\nExample OpenAPI:\r\n```yaml\r\nopenapi: 3.0.3\r\ninfo:\r\n  title: 'Example'\r\n  version: 0.1.0\r\nservers:\r\n  - url: 'http://example.com'\r\npaths:\r\n  '/foo':\r\n    delete:\r\n      responses:\r\n        '200':\r\n          description: OK\r\ncomponents:\r\n  schemas:\r\n    Brother:\r\n      type: object\r\n      properties:\r\n        sister:\r\n          $ref: '#/components/schemas/Sister'\r\n    Sister:\r\n      type: object\r\n      properties:\r\n        brother:\r\n          $ref: '#/components/schemas/Brother'\r\n```\r\nGenerator produces warnings and models package is empty.\r\n```bash\r\nCould not find reference in parsed models or enums\r\nReference(ref='#/components/schemas/Sister')\r\n\r\nCould not find reference in parsed models or enums\r\nReference(ref='#/components/schemas/Brother')\r\n```\r\n\r\nI expect the generated models for `Brother` and `Sister`. Something like:\r\n```python\r\n# models/brother.py\r\nclass Brother:\r\n    sister: Union[Unset, Sister] = UNSET\r\n\r\n# models/sister.py\r\nclass Sister:\r\n    brother: Union[Unset, Brother] = UNSET\r\n```\r\n","author":{"url":"https://github.com/mtovts","@type":"Person","name":"mtovts"},"datePublished":"2021-08-13T08:30:26.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":11},"url":"https://github.com/466/openapi-python-client/issues/466"}