Update/extend faust_prod_opt module and its use; mostly adding the DYNPROG method.

- Simplifying Faust::multiply_order_opt_all_best using gemm_gen and handle transpose/adjoint cases.
- Enabling use of DYNPROG method in TransformHelper::get_product and multiply(MatDense).
- TransformHelper::get_product: fixing issue on mul_order_opt_mode argument default value, to prevent using always the DEFAULT method.
- Update of pyfaust/matfaust.FaustMulMode to enable the DYNPROG meth and its doc.
- FaustCore.set_FM_mul_mode has now a silent argument.