eja: move away from using matrices as our "multiplication table."

eja: move away from using matrices as our "multiplication table."

Instead of passing around a bunch of matrices that can be applied to
vectors to figure out how multiplication works, it's simpler (and
probably faster) to use a two-dimensional array whose (i,j)th entry
contains the answer to "how do we multiply basis elements i and j?"

When we feed these arrays into the EJA constructor, they must contain
vectors: there's no algebra yet, so it's not like we have any algebra
elements to pass in. However, in the long run, it's much more
convenient to have the multiplication table *stored* in terms of
algebra elements; that way we don't have to convert back and forth
every time we want to multiply two algebra elements. The algebra
constructor now performs this conversion and stores a table containing
algebra elements. This makes product_on_basis() a simple table lookup.