This reverts commit ccaaad19.

Make vec::view a method too.

tutorial: changing `again` to `loop`

Destructors were internally declared with an extra (hidden) nil-typed
argument that was passed in by-ref mode. This was causing spurious
mode warnings. Deleted it. Also some misc. cleanup because I
couldn't help myself.

This section associates borrowed pointers purely with stack allocation, which
is confusing. The following sections explain pointers in detail.