3D Axis
~~~~~~~
The previous constructor of `.axis3d.Axis`, with signature
``(self, adir, v_intervalx, d_intervalx, axes, *args, rotate_label=None, **kwargs)``
is deprecated in favor of a new signature closer to the one of 2D Axis; it
is now ``(self, axes, *, rotate_label=None, **kwargs)`` where ``kwargs`` are
forwarded to the 2D Axis constructor.  The axis direction is now inferred from
the axis class' ``axis_name`` attribute (as in the 2D case); the ``adir``
attribute is deprecated.

The ``init3d`` method of 3D Axis is also deprecated; all the relevant
initialization is done as part of the constructor.

The ``d_interval`` and ``v_interval`` attributes of 3D Axis are deprecated; use
``get_data_interval`` and ``get_view_interval`` instead.
