Transition to using fixed size arrays for dimensions

[bluss]

Main win is syntax, array[[1, 2]] is pretty sweet.

[bluss]

Indices of such added in #34, but it's just a step.

[bluss]

I'm working on fixed size array dimension now. In concrete, [usize; 2] is used instead of (usize, usize) and so on.

• Simpler and sounder dimension code. Generalize to integer generic parameters (assuming that will happen before variadic generics!)
• We can allow more operations on array shapes, in the way that was proposed by @b52

PSA: Switching to the explicit size aliases like Ix1, Ix2, Array1, Array2 will make your code mostly ready for the transition. Generic code (Array<A, D> where D: Dimension) should not need any change.

[AtheMathmo]

I have considered making the opposite change a few times. I agree that arr[(1,2)] looks pretty clunks but it has the advantage of being able to do Range indexing properly, i.e. arr[(.., 2)]. Are you planning on just removing this type of indexing or do you have some plan to do it with fixed size arrays?

[bluss]

Ok, the description of the issue in the first post here is a red herring -- the syntax used in indexing is already achieved using conversion traits and that part is "easy". I understand that heterogenous tuples would make interesting things (however do note that Index/IndexMut don't support custom view types, so we don't have much fun there).

The big change here is going to 2d Arrays (for exampmle) as Array<f32, [usize; 2]> or maybe Array<f32, Dim<[usize; 2]>> (of course there are type aliases for the dimensionalities).