Change hide shortcut to toggle shortcut.

This saves the windows either (preferably) above or (less preferably, and probably uselessly) below Shroud's backdrop, then attempts to restore Shroud in the same position.

You can use this like the "Show Desktop" toggle in Exposé/Mission Control to temporarily peek at items behind Shroud, but you can also use it to put additional windows in front of the backdrop.  Hide the backdrop, bring other windows/applications to the front, then show the backdrop again; it'll still be behind the original rearmost window but now also behind your other windows.