Allow for control points which do not lie on a single axis

[Martin von Gagern]

Particularly when laying out loops, it might be desirable if the inbound and the outbound direction of a simple "pass-through" (i.e. one covariant and one contravariant index) tensor wouldn't have to lie on the same line. Or as an alternative, there should be some other way to format a clearly visible loop which doesn't collapse to a single line.