add in stretch equations to placement
add in stretch equations to placement

Eric89GXL/vispy,drufat/vispy,michaelaye/vispy,drufat/vispy,michaelaye/vispy,drufat/vispy,Eric89GXL/vispy,ghisvail/vispy,Eric89GXL/vispy,michaelaye/vispy,ghisvail/vispy,ghisvail/vispy