plsdidev: Set parameters that define current device-space window

Set relative margin width, aspect ratio, and relative justification that define current device-space window. 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. If plsdidev is not called the default values of mar, jx, and jy are all 0. aspect is set to a device-specific value.

mar (PLFLT, input) Relative margin width. aspect (PLFLT, input) Aspect ratio. jx (PLFLT, input) Relative justification in x. Value must lie in the range -0.5 to 0.5. jy (PLFLT, input) Relative justification in y. Value must lie in the range -0.5 to 0.5.

Redacted form: plsdidev(mar, aspect, jx, jy)

This function is used in example 31.