BDM degree 0

[mscroggs]

You can currently create a degree 0 BDM element on a triangle:

e = basix.create_element(basix.ElementFamily.BDM, basix.CellType.triangle, 0)

This gives an element with 3 DOFs, probably the same as an RT degree 1 element.

The lowest degree BDM element is usually the degree 1 element with 6 DOFs. Trying to create a degree 0 BDM element should probably throw a runtime error.