rename function dim -> dims

[nickrobinson251]

I know this is a bike-shed-y naming issue, but...

I think dims would be really nice, to go with ndims, permutedims, dropdims, etc.

We might have to do something ugly in the source code, like write NamedDims.dims all over or define an alias like const _dims = dims, but it might be worth doing if it's a nicer API for the user.

[oxinabox]

The main use of the dim function is dim(A, :x)==1 though.

[nickrobinson251]

it's a fair point - lets leave this open to see if anyone else has an opinion, and otherwise keep as is?

[oxinabox]

when #21 is merged this can likely be closed as the version of the function that returns NamedTuples of the function will be gone.

Though the version that accepts tuples dim((:a, :b)) = (1,2)
will remain,
so maybe there is still an argument to have this called dims?

[nickrobinson251]

I'm happy enough for this to stay as dim :)