Underworld

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New functionality:
* Timing module for high level profiling.
* Scaling module for numerical value scaling.
* Index set objects can now directly index numpy arrays.
* `show_grid()` image rendering.

Changes:
* glucifer Surface defaults to use onMesh=True.
* added `data` handle to swarm as shortcut to particle coordinates data.
* Adding aliases for mesh vertex sets (left,right,etc)
* Removed `unsupported` subrepo.
* Docker images switch to MPICH for Shifter compatibility at magnus.

Documentation:
* Examples reorganised.
* All examples now include quantitative tests.
* Moved many examples to models library repo.
https://github.com/underworldcode/model_library
* Added new example, 08_Uplift_TractionBCs.ipynb.
* Moved benchmarks and tutorials to models library repo.
* Relocated defunct models:
https://github.com/underworldcode/model_graveyard
* Big overhaul of user guide.
* User guide rendered to html for Readthedocs page.
* Updates for docstrings and doctests.
* Improved error messaging.

Fixes:
* Fix incorrect particle outside domain issue 335
* Other stability improvements.

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* Remove `warning` module visibility from top level underworld
module.

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Enhancements:
* Removed submodules in favour of direct access.
* Petsc-3.9.x compatible.
* Support for nested SafeMaths operations.
* Improved function error messaging.

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Documentation:
* Fixes for Sphinx API documentation generation.

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New features:
* New 'long' type swarm variable.
* User provided post-solve callback functionality added.

Enhancements:
* Speed up (minimum 5x) for SwarmVariable reload.
* Petsc-3.8 compatible.
* Non root dockerfile now.

Documentation:
* Viscoelastic tutorial, see ./docs/tutorials/
* Update raijin and magnus build instructions.

API Changes:
* New interface for a MeshVariable, mesh.add_variable().
* New interface to Integrate, mesh.integrate().

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* Updating release to the correct version of lavavu