Piccolo

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* Added missing type annotation for ``run_sync``.
* Updating type annotations for column default values - allowing callables.
* Replaced instances of ``asyncio.run`` with ``run_sync``.
* Tidied up aiosqlite imports.

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* Added JSON and JSONB column types, and the arrow function for JSONB.
* Fixed a bug with the distinct clause.
* Added ``as_alias``, so select queries can override column names in the
response (i.e. SELECT foo AS bar from baz).
* Refactored JSON encoding into a separate utils file.

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* Removed old iPython version recommendation in the ``piccolo shell run`` and
``piccolo playground run``, and enabled top level await.
* Fixing outstanding mypy warnings.
* Added optional requirements for the playground to setup.py

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* Added ``piccolo sql_shell run`` command, which launches the psql or sqlite3
shell, using the connection parameters defined in ``piccolo_conf.py``.
This is convenient when you want to run raw SQL on your database.
* ``run_sync`` now handles more edge cases, for example if there's already
an event loop in the current thread.
* Removed asgiref dependency.

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* Queries can be directly awaited - ``await MyTable.select()``, as an
alternative to using the run method ``await MyTable.select().run()``.
* The ``piccolo asgi new`` command now accepts a ``name`` argument, which is
used to populate the default database name within the template.

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* Centralised code for importing Piccolo apps and tables - laying the
foundation for fixtures.
* Made orjson an optional dependency, installable using
``pip install piccolo[orjson]``.
* Improved version number parsing in Postgres.

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