Extend bitslice multiplication to e=3,4,...

[Martin Albrecht]

Bit-sliced multiplication is only implemented for GF(2^2). However, at least for very small //e//, it is more efficient than the standard implementation of matrix multiplication.Thus, it should also be implemented for bigger //e//. Note that either a more clever way of coming up with multiplication formulas must be implemented first or a separate formula for each modulus must be implemented.

[Martin Albrecht]

6a614c5f264b this now works up to e=8.