Piccolo-api

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Renaming migrations which were problematic for Windows users.

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Using Pydantic to serialise the ``PiccoloCRUD.new`` response. Fixes a bug
with serialising some values, such as ``decimal.Decimal``.

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* Using Piccolo's ``run_sync`` instead of asgiref.
* Loosened dependencies.
* ``create_pydantic_model`` now supports lazy references in ``ForeignKey``
columns.
* MyPy fixes.

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* ``PiccoloCRUD`` now supports the `__readable` query parameter for detail
endpoints - i.e. `/api/movie/1/?__readable=true`. Thanks to sinisaos for
the initial prototype.
* Improving type hints.

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Bumped requirements.

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Using ``Column._meta.required`` for Pydantic schema.

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