consistently use attribute with vs. @with
Combiner.none was confusing, get rid of it.

'none' could imply 'no operation', which it actually did, an empty array, or a
nil value.  Depending on what was actually expected, use either
  :array
or
  :literal, value: []
or
  :literal, value: nil
Get rid of weird required :literal argument, but stay 2.0.0 compatible