Map Between World and Device Coordinates

USAGE:
device.xy(wx, wy)
world.xy(dx, dy)
dx,dy:
vectors of x- and y-coordinates in the current device coordinate system.
wx,wy:
vectors of x- and y-coordinates in the current world or user coordinate system.

VALUE:
a list with elements named x and y that give the mapped coordinates, i.e., device coordinates for device.xy and world coordinates for world.xy.