Clean-up tests.
Project MMS test added.
Make list handling in convergence tests more pythonic.
Enable auto layer even spacing in extruded mesh coordinate generation.
Directly extract NumPy data pointer for dofs_per_column

Getting the pointer as an int is not always safe and can lead to an
OverflowError exception when the address is too large to convert.
Merge pull request #13 from firedrakeproject/extrusion

* Adds projection MMS test. (closes #3)
* Makes even spaced extrusion easier (closes #8)
* Fixes a bug in extracting the dofs_per_column NumPy array data