Quad and hex mesh generation naming

[Ivan Yashchuk]

Names UnitQuadMesh and UnitHexMesh do not follow the convention that the name describes the domain, as these names say more about the cell shape than the domain.

It might be better to have it as

UnitSquareMesh.create(m, n, cell = "quadrilateral")
UnitCubeMesh.create(m, n, k, cell = "hexahedron")

with defaults set to triangle or tetrahedron cells.

[Prof Garth Wells]

Should we use strings or enums? I like enums because they provide tab-completion with interactive Python.

[Prof Garth Wells]

In progress in https://bitbucket.org/fenics-project/dolfin/branch/garth/fix-issue-898-quad-hex-mesh.

[Jan Blechta]

@garth-wells, do you plan to finish this before release?

@chris_richardson, this still in my opinion marked correctly as a release blocker.

[Chris Richardson]

I've set the branch to test on bamboo. Not sure if it needs more work, or if it can just be merged.

[Jan Blechta]

This should be even more abstract:

UnitCubeMesh(std::vector<std::size_t> sizes,
             CellType::Family cell_family=CellType::Family::Simplex,
             std::string diagonal="right")

UnitCubeMesh({{64}})                              # intervals
UnitCubeMesh({{16, 16}})                          # triangles
UnitCubeMesh({{16, 16}}, CellType::Family::Cube)  # quads
UnitCubeMesh({{4, 4, 4}})                         # tetrahedrons
UnitCubeMesh({{4, 4, 4}}, CellType::Family::Cube) # hexes