clarify permutedims docs

[stevengj]

As commented on discourse, it would be nice if the permutedims examples began with something like an array of strings where transpose is inapplicable.

This PR simply clarifies the docs and adds a few more examples.

[stevengj]

Pursuant to the discussion above, I merged the docstrings for permutedims(A::Array, perm) and permutedims(A::AbstractMatrix), since the latter is just a special case of the former with perm = (2,1).

[stevengj]

Bump.

[jishnub]

Looks good to me, and it's a clear improvement