Piccolo

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Modified the exit codes for the ``forwards`` and ``backwards`` commands when no
migrations are left to run / reverse. Otherwise build scripts may fail.

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* Improved the method signature of the ``output`` query clause (explicitly
added args, instead of using ``**kwargs``).
* Fixed a bug where ``output(as_list=True)`` would fail if no rows were found.
* Made ``piccolo migrations forwards`` command output more legible.
* Improved renamed table detection in migrations.
* Added the ``piccolo migrations clean`` command for removing orphaned rows
from the migrations table.
* Fixed a bug where ``get_migration_managers`` wasn't inclusive.
* Raising a ``ValueError`` if ``is_in`` or ``not_in`` query clauses are passed
an empty list.
* Changed the migration commands to be top level async.
* Combined ``print`` and ``sys.exit`` statements.

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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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