Allow element to be positioned absolute

[ppowalowski]

If the element which is to be sticked is positioned absolute, several issues pop up:

• placeholder is not positioned absolute
• width is not synced properly

[theenoahmason]

Also experiencing this issue. very important.

A couple ways around this that would help me right now:

• placeholder should not be added if element is already absolute when document is loaded.
• placeholder should load with height: 0; if element is already absolue when document is loaded.
• placeholder should have a class ie: "stickUpPlaceholder" to allow us to manipulate it accordingly.
  this should probably happen anyway. there is no way to properly target the placeholder div.

Excellent job by the way. Really loving it!

[ppowalowski]

@theenoahmason Can you work out a pull request targeting this enhancement? I am quite involved currently so any help would be of great value :-)