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. Refactor the current ungodly fast charpoly hack (relies on the
   theory to ensure that the charpolys are equal.)