qmat follows other type conventions (T, N, M) and is annotated differently so it's not as confusing to follow
Removed qmat::operator[] - it's not clear from calling it that it's column-major (as evidenced by the comments needing to explicitly make clear at call sites that it's column, not row), so I've collapsed them into two separate functions that explicitly fetch either a column or a row. This also ties them nicely into qvec<N>.