Add side boundary conditions for the bottom layer only.
Extruded facet map computation occurs over a layered set.
Add offset to the extruded boundary node map.
Add strong side boundary conditions for extruded meshes.
Extend strong BCs to the LHS. Add new xfailing test for side bcs.
Eliminate some of the extruded mesh special casing.
Add exterior and interior _Facet object construction for extruded meshes.
Set up correct mesh size to have at least one interior dof and space to CG 2.
Add docstring for layers property.
Change test boundaries and update doc strings.
Change the strong bcs test case to use the initial expression.
Extrusion side strong BCs test now passes.
Add a geometric_dimension property to extruded meshes

Additionally, fix the calculation of the facet dimension in the extruded
case.
Fix test description.
Add docstring to layers property.
Make test more pythonic.
Handle the case when the mesh has no exterior facets.
Add test boundary checking on 2D quad extruded mesh.
Fix lint issue.
Extend extruded facets tests slightly

Generalise existing tests and add test that the area of an extruded
interval is correct.