Skeleton updates

[lkdvos]

This PR brings the package up to date with skeleton v0.2.0

Some notes/todos, probably for different PRs:

• the design with LinearAlgebra.qr(::AbstractArray, ::Tuple, ::Tuple, ::Tuple) is both piracy and a large (40+) source of ambiguities, because LinearAlgebra tends to specialize according to qr(::StructuredArray, args...). Because I'm not so familiar with what this signature is specifically used for, I was wondering if it would be possible to only define this in terms of LinearAlgebra.qr(::AbstractArray, ::BlockPermutation) and do the other dispatch manually.
• it wasn't clear to me if the intention for the LinearAlgebra extensions is to really be an extension, or simply defined in the main package.

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[mtfishman]

Thanks for the comments, those are both good points to discuss. Can you raise those as separate issues?

As a short answer, that signature of qr is meant to be a labelled tensor version of QR, i.e. qr(a, (:i, :j, :k), (:i, :j), (:k)), but probably that can just make use of NamedDimsArrays, i.e. qr(nameddims(a, (:i, :j, :k)), (:i, :j), (:k,)), and the reason the signature is so generic is because we want to allow any objects as dimension names.

Another alternative is to use a wrapper type like Name to disambiguate in these cases, i.e. we could require inputs like qr(a, Name.((:i, :j, :k)), Name.((:i, :j)), Name.((:k,))), if you want to use dimension names/labels as opposed to BlockPermutation, which is a bit of a lower level interface.