Piccolo

------
Added ``Bytea`` / ``Blob`` column type.

-------------------------------------------------------------------------------

-------
Fixing a bug with migrations which drop column defaults.

-------------------------------------------------------------------------------

-------
* Fixing a bug where re-running ``Table.create(if_not_exists=True)`` would
fail if it contained columns with indexes.
* Raising a ``ValueError`` if a relative path is provided to ``ForeignKey``
``references``. For example, ``.tables.Manager``. The paths must be absolute
for now.

-------------------------------------------------------------------------------

-------
Fixing a bug with ``Boolean`` column defaults, caused by the ``Table``
metaclass not being explicit enough when checking falsy values.

-------------------------------------------------------------------------------

-------
* The ``ForeignKey`` ``references`` argument can now be specified using a
string, or a ``LazyTableReference`` instance, rather than just a ``Table``
subclass. This allows a ``Table`` to be specified which is in a Piccolo app,
or Python module. The ``Table`` is only loaded after imports have completed,
which prevents circular import issues.
* Faster column copying, which is important when specifying joins, e.g.
``await Band.select(Band.manager.name).run()``.
* Fixed a bug with migrations and foreign key constraints.

-------------------------------------------------------------------------------

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

-------------------------------------------------------------------------------