11. Figure out if CombinatorialFreeModule's use of IndexedGenerators
can be used to replace the matrix_basis().
+
+12. Move the "field" argument to a keyword after basis, jp, and ip.
+
+13. Instead of storing the multiplication and inner-product tables in
+ RationalBasisEuclideanJordanAlgebra, why not just create the
+ algebra over QQ in the constructor and save that? They're globally
+ unique, so we won't wind up with multiple copies.