Mulgen

as per #54 

I agree with @kortschak . We should panic if it's just some random number. 

Do we want to have our own constants in mat64 (aka mat64.Transpose)? It seems desirable that users never have to interface with blas beyond registering. It would also avoid the problem where blas actually accepts ConjTrans as a valid input for DXxx cases. Instead, we define

const (
    NoTrans = blas.NoTrans
    Trans = blas.Trans
)

and now it's logical to panic on ConjTrans because ConjTrans doesn't exist in mat64