newRPL: Simplified matrices proposal

[3298]

I see you already covered vectors in cylindrical or spherical modes (which I was going to voice concerns about). Your solution looks pretty good.
But I found another potential source of trouble: the SIZE command behaves differently on matrices and vectors: on matrices it obviously returns both dimensions as a list with two elements, on a vector or any other array it returns a list with just a single element. This may cause compatibility problems when vectors cannot be distinguished from single row or single-column matrices anymore.
I'd vote for a distinction between 1D and 2D arrays. Keeping the old "hack" for vectors should be simple (vectors and other 1D arrays are stored as 2D arrays with 0 as second dimension; this is how they can share the DOARRY prolog). Other than the SIZE issue, that's more of a personal preference, though.