Special case request for Not() about dataframesmeta.jl

[MatthewRGonzalez]

I agree that a special case for Not() is necessary. This request is similar to #283, which proposes—among other changes—the use of @select df Not(:a) as opposed to the current solution of @select df $(Not(:a)). With this in mind, two potential designs for this implementation are

@chain df begin
     @select @not :Col1 :Col2 ...
end

and

@chain df begin
     @select Not([:Col1, :Col2, ...])
end

I prefer @not as I believe it looks cleaner, buy am curious as to whether there are additional considerations regarding this proposal.