The reference type, `RefBase<A, D, R>`, is parameterized by its elementtype, a dimensionality type, and its "referent" type. This last typeis only a `PhantomData` marker, and acts to differentiate referencesthat are "safe" from those that are "raw", i.e., references that comefrom an array whose storage is `Data` vs an array whose stoarge is`RawData`. The `DerefMut` implementation contains a check of uniqueness,guaranteeing that an `&mut RefBase` is safe to mutate.This comes with one breaking change and one important internal librarynote. The breaking change is that `ArrayBase` no longer implements `Copy`for views. This is because a `RefBase` does not know where it is pointing,and therefore cannot implement `Copy`; this, in turn, prohibits`ArrayBase` from implementing `Copy`. Users will now have to explicitlyinvoke `Clone` in the same way that they do for non-view arrays.The important library note has to do with the `.try_ensure_unique` checkthat occurs in the `DerefMut` implementation. The library's methods areallowed to *temporarily* break the invariant that an array's `ptr`is contained within `data`. The issue comes when trying to then alter`ptr`, `shape`, or `dim` while that invariant is broken. Code wasusing `self.ptr = ...` (where `self` is `ArrayBase`), which triggers`DerefMut`, which calls `try_ensure_unique`, which panics on thepointer inbounds check. As a result, code that is altering `RefBase`fields while the array's invariants are broken must be sure to write`self.aref.ptr = ...` instead.

… Copy

…to RefBase and LayoutRef

…ow to write functionality with the new types

… bullets on the new types

I think I accidentally moved this over to ArrayRef, but we're not sure it should still require DataOwned