plsdidev: Set window into device space using margin, aspect ratio, and justification.

Set window into device space using margin, aspect ratio, and justification. If you want to just use the previous value for any of these, just pass in the magic value PL_NOTSET. It is unlikely that one should ever need to change the aspect ratio but it's in there for completeness.

mar (PLFLT, input) NEEDS DOCUMENTATION aspect (PLFLT, input) NEEDS DOCUMENTATION jx (PLFLT, input) NEEDS DOCUMENTATION jy (PLFLT, input) NEEDS DOCUMENTATION