Add generic initializers for statically-dimensioned array types

[thatcomputerguy0101]

This takes advantage of const generics to provide general initializers for the statically-dimensioned array types. (2-6 dimensions, with the current implementations). This reduces the reliance on macros for array initialization, and enables other crates to operate more succinctly when working with an unknown-dimension static array type. I'm unsure how well this fits with the existence of the dynamic array index implementation, and the name of the new type alias IxD is open for discussion. No additional test cases have been implemented for this functionality yet.

[bluss]

Hm, new clippy lints should be fixed in a different PR, I think

[thatcomputerguy0101]

I originally decided on the name IxD to match the style of Ix0, Ix1, etc..., but with a generic D instead of a fixed value. It is also short, which helps in its usability as a convenience type (since it is an alias for Dim<[Ix, D]>). However, its name is close to IxDyn, and I have concerns about possible confusion between those two.