Add operator @ for matrix multiplication

@H2CO3 I see there is Add a matrix multiplication operator like Python? about mat_mul is not commonly used. Would you please elaborate on the drawbacks?

@scottmcm

Can you speak to why you think it's needed?

Why not? For Python people switching to Rust, it's a welcome sign.

What's wrong with overloading * to work with matrices too?

Maybe a half-second hold back for people new to a library, is it an element-wise or matrix multiplication?