Strongly typed `Axis` arguments

[bluss]

We could have strongly typed Axis arguments (instead of current usize).

It even allows mixing dynamically bounds checked axis numbers and statically checked ones:

.subview(Axis(0), 1) vs. .subview(Axis0, 1) would both be possible at the same time.

[vbarrielle]

Yes that's really a nice feature to have, imo it improves readability and prevents some mistakes. Axis0 would be exposed as a constant?

[bluss]

Yes. Using generics is unfortunate in one way, since it makes the interface seem more complicated. But it also enables static checking. I've tested this out at some point, and I think it works.

[bluss]

Oh I think it requires O(n²) impl blocks where n is the number of dimensions supported though (We have up to 12-tuples).

[vbarrielle]

Maybe macros can help on that point, but I wouldn't know, I've not written many macros yet.

[bluss]

Fixed by #97