This argument forces the textbox position, meaning it won't be moved
to be inside of the bounds of the screen (nor have the 10 pixel padding
on each side.)
Currently, you can change platform speed, but not enemy speed, which is
always hardcoded to be 4. This commit fixes that, by adding the
"enemyv" property, which is an offset to the speed of 4. Since it
defaults to 0, older levels are not broken by this change.