can.ui.Position API

## Purpose
- keep one element relative to another element
## Learn from
- http://jqueryui.com/demos/position/
## Options
- my : "left top",
- at : "right top",
- of : "#bar",
- from - By default, a position is moved to scroll with whatever it is positioned relative to. From should be able to change this.
- offset : "50 50",
- collision : "flip"
## Events
- move - if it needs to change locations, it should tell other widgets
- destroy - should set back element in original position
## Methods
- update options
## Theming
## Examples
- tooltips
- tooltip on a scrolling grid.
- simple dialog
## Notes
- we might need to know if the `of` element is no longer visible b/c of scrolling.