Piccolo

------
Loosen the ``typing-extensions`` requirement, as it was causing issues when
installing ``asyncpg``.

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Added ``nested`` output option, which makes the response from a ``select``
query use nested dictionaries:

.. code-block:: python

>>> await Band.select(Band.name, *Band.manager.all_columns()).output(nested=True).run()
[{'name': 'Pythonistas', 'manager': {'id': 1, 'name': 'Guido'}}]

Thanks to wmshort for the idea.

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Added ``to_dict`` method to ``Table``.

If you just use ``__dict__`` on a ``Table`` instance, you get some non-column
values. By using ``to_dict`` it's just the column values. Here's an example:

.. code-block:: python

class MyTable(Table):
name = Varchar()

instance = MyTable.objects().first().run_sync()

>>> instance.__dict__
{'_exists_in_db': True, 'id': 1, 'name': 'foo'}

>>> instance.to_dict()
{'id': 1, 'name': 'foo'}

Thanks to wmshort for the idea, and aminalaee and sinisaos for investigating
edge cases.

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------
Removed problematic type hint which assumed pytest was installed.

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------
Minor changes to ``get_or_create`` to make sure it handles joins correctly.

.. code-block:: python

instance = (
Band.objects()
.get_or_create(
(Band.name == "My new band")
& (Band.manager.name == "Excellent manager")
)
.run_sync()
)

In this situation, there are two columns called ``name`` - we need to make sure
the correct value is applied if the row doesn't exist.

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------
``get_or_create`` now supports more complex where clauses. For example:

.. code-block:: python

row = await Band.objects().get_or_create(
(Band.name == 'Pythonistas') & (Band.popularity == 1000)
).run()

And you can find out whether the row was created or not using
``row._was_created``.

Thanks to wmshort for reporting this issue.

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