Outer product

[termoshtt]

Restore outer product removed in #41

[termoshtt]

We can use ndarray::linalg::Dot to calc outer product:

let a: Array1<f64> = random(3);
let b: Array1<f64> = random(4);
let a = into_col_vec(a);
let b = into_row_vec(b);
let ab = a.dot(&b);

but this gives Array2<A> only (i.e. it cannot generate RcArray2<A> without into_shared).
Generalized Dot #39 will help this.

[termoshtt]

transfer to #29