Array interface refactoring

[Ben Rudiak-Gould]

While we're on the topic, I have a couple of problems with the current array 
system that cut deeper than the naming:

     * The function for getting the bounds of an MArray is pure, so the
       interface can't accommodate resizable arrays.

     * unsafeAt, unsafeRead and unsafeWrite take 0-based indices, and the
       bounds checking and conversion is handled externally, based on the
       bounds you return. This means the interfaces can't support array
       windowing, at least in the multidimensional case. I'd be happy with
       windowing for one-dimensional arrays only, but there's no way to
       restrict your array type to one-dimensional index types.

-- Ben