Handle the authorial interventions in a similar way to the original

[federicaspinelli]

When encoding <del rend="overstrike"> and <add place="supralinear">, the addition is showed near the deletion anyway; trying to create a diplomatic edition, it could be useful to show the addition where it is in the text, above the deleted text and not alongside; see this image f.i.:

[gmarozzi]

When encoding <del rend="overstrike" and <add place="supralinear", the addition is showed near the deletion anyway; trying to create a diplomatic edition, it could be useful to show the addition where it is in the text