PR Summary

Just a draft for now, but this is meant to be substantially simpler than the currentconstrained_layout and more robust. Some of the flakiness should be gone. Colorbars are better located, and respect their anchors now.

This version includes the idea offigure.sub_panels, but that could be (reluctantly) taken out if its deemed not useful. It does get you nice things like:

It wold have been nice to do them separately but it was pretty hard to make sure everything works for the nesting....

Most of the constrained_layout baseline images have changed, but thats because colorbar sizing has changed (for the better), and small changes to how padding is handled. I don't feel any of the choices made here make any of the images worse, and I don't think its worth trying to make them the same. I could be convinced to change a lot of these to assertions on the position of the axes, but its then a challenge to see what goes wrong if they break.

• check colorbar aspect
• tests for subpanel...
• modify tutorial and docstring
• add tutorial forsubpanel.
  • modify transform tutorial

PR Checklist

• Has Pytest style unit tests
• Code isFlake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way