Add support for resizing proportionally by setting a dimension to < 0
Add support for resizing proportionally by setting a dimension to < 0

etix/magick,zuriu/magick,500px/magick,rainycape/magick,zuriu/magick,500px/magick,etix/magick,500px/magick,rainycape/magick,etix/magick,rainycape/magick,zuriu/magick