## Feature #10445

### [PATCH 3/3] Extend Matrix#[]

**Description**

I've made patches which Matrix#[] returns new vector if either arguments is range,

and returns new matrix, if both arguments are range.

Like below.

```
# matrix[row, column] -> obj or nil
# matrix[row, col_range] -> new_vector or nil
# matrix[row_range, column] -> new_vector or nil
# matrix[row_range, col_range] -> new_matrix or nil
Matrix.diagonal(9, 5, -3)[1, 1]
=> 5
Matrix.diagonal(9, 5, -3)[1, 0..1]
=> Vector[0, 5]
Matrix.diagonal(9, 5, -3)[0..1, 0]
=> Vector[9, 0]
Matrix.diagonal(9, 5, -3)[0..1, 0..1]
=> Matrix[[9, 0], [0, 5]]
```

I'm not sure `matrix[row, col_range]`

should return `vector`

or `matrix`

But from my view, it's fine.

I'm not in a hurry. Take your time.

**Files**