Merge branch 'mcflugen-add-rectilinear-grid'
Added submodules for sphinx documentation.
Removed _themes folder.

Removed
=======
* Removed _themes folder from the repository as we're now using the
  submodule, sphinx-scipy-theme.
Changed to use submodules.
Fixed some numbered-list formatting.
Build documentation as part of testing.
Merge branch 'add-submodule-for-docs' of https://github.com/mcflugen/landlab into mcflugen-add-submodule-for-docs

Conflicts:
	.travis.yml
Merge branch 'mcflugen-add-submodule-for-docs'