added method that lets caller specify relation between spaced views

original method now calls the new one with NSLayoutRelationGreaterThanOrEqual as before

@ndonald2 I needed this functionality to have some labels display correctly when not pinning their widths; otherwise they'd shrink due to the >= relation of the spacing. This way I can set it to =
I agree with @ndonald2 that no threat is required.

By the way, `obseleted` seems to require an availability statement, and thus version numbers. Deprecated can stand alone.