1. Add CartesianProductEJA.

2. Check the axioms in the constructor when check != False?

3. Add references and start citing them.

4. Implement the octonion simple EJA.

5. Factor out the unit-norm basis (and operator symmetry) tests once
   all of the algebras pass.

6. Implement spectral projector decomposition for EJA operators
   using jordan_form() or eigenmatrix_right(). I suppose we can
   ignore the problem of base rings for now and just let it crash
   if we're not using AA as our base field.

7. Do we really need to orthonormalize the basis in a subalgebra?
   So long as we can decompose the operator (which is invariant
   under changes of basis), who cares?

8. Check that our field is a subring of RLF.