Calendar should center on input box

[dankolz]

The calendar looks like it is absolutely positioned with the left of the calendar roughly aligned with the left of the input element used to hold the date.

What we'd like to do is have it align to the center of the input box.

In playing with the code, it looks like the easiest way to do this to add a layout option to rome and a separate option to bullseye to get the center x position of the element instead of the left x position.

If you'd be willing to merge something like this, I'd be happy to write it today.