ENH: Constrained layout geometry manager

doc/api/api_changes/2017-09-29_JMK_constrained_layout_api.rst

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+API changes for ``constrained_layout``
+----------------------------------------
+
+The new constrained_layout functionality has some minor (largely backwards-
+compatible) API changes.  See
+:ref:`sphx_glr_tutorials_intermediate_constrainedlayout_guide.py` for
+more details on this functionality.
+
+This requires a new dependency on kiwisolver_.
+
+_https://github.com/nucleic/kiwi
+
+kwarg ``fig`` deprectated in `.GridSpec.get_subplot_params`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Use ``figure`` instead of ``fig``, which is now deprecated. 

doc/users/next_whats_new/constrained_layout.rst

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+Constrained Layout Manager
+---------------------------
+
+.. warning::
+
+    Constrained Layout is **experimental**.  The
+    behaviour and API are subject to change, or the whole functionality
+    may be removed without a deprecation period.
+
+
+A new method to automatically decide spacing between subplots and their
+organizing ``GridSpec`` instances has been added.  It is meant to
+replace the venerable ``tight_layout`` method.  It is invoked via
+a new ``constrained_layout=True`` kwarg to
+`~.figure.Figure` or `~.figure.subplots`.
+
+There are new ``rcParams`` for this package, and spacing can be
+more finely tuned with the new `~.set_constrained_layout_pads`.
+
+Features include:
+
+  - Automatic spacing for subplots with a fixed-size padding in inches around
+    subplots and all their decorators, and space between as a fraction
+    of subplot size between subplots.
+  - Spacing for `~.figure.suptitle`, and colorbars that are attached to
+    more than one axes.
+  - Nested `~.GridSpec` layouts using `~.GridSpecFromSubplotSpec`.
+
+  For more details and capabilities please see the new tutorial:
+  :doc:`/tutorials/intermediate/constrainedlayout_guide`
+
+Note the new API to access this:
+
+New ``plt.figure`` and ``plt.subplots`` kwarg: ``constrained_layout``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+:meth:`~matplotlib.pyplot.figure` and :meth:`~matplotlib.pyplot.subplots`
+can now be called with ``constrained_layout=True`` kwarg to enable
+constrained_layout.
+
+New ``ax.set_position`` behaviour
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+:meth:`~matplotlib.axes.set_position` now makes the specified axis no
+longer responsive to ``constrained_layout``, consistent with the idea that the
+user wants to place an axis manually.
+
+Internally, this means that old ``ax.set_position`` calls *inside* the library
+are changed to private ``ax._set_position`` calls so that
+``constrained_layout`` will still work with these axes.
+
+New ``figure`` kwarg for ``GridSpec``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In order to facilitate ``constrained_layout``, ``GridSpec`` now accepts a
+``figure`` keyword.  This is backwards compatible, in that not supplying this
+will simply cause ``constrained_layout`` to not operate on the subplots
+orgainzed by this ``GridSpec`` instance.  Routines that use ``GridSpec`` (e.g.
+``fig.subplots``) have been modified to pass the figure to ``GridSpec``.