Support IxDyn/vec![] dimension better

[bluss]

• mutate in place stepping for the iterator
• Pass index as slice
• allow indexing with regular arrays (The great dimension migration to Dim<[Ix; N]> #225)
• No allocation for small case Reimplement IxDyn #285 Reimplement IxDyn, with no allocation for the small dimension case #301
• .zip_mut_with improvement reduces binary operation custom stride case overhead for ixdyn Reimplement rows case in zip_mut_with using Zip #292
• Fancier slicing, selecting subviews Support subviews in slice s! syntax #215

[nilgoyette]

Closing this issue

• It is unclear what mutate in place stepping for the iterator means but I think this feature is long done and we simply forgot to close it. Feel free to open it again, although with more details.