Key Bindings: Modifier Only *Double* Keypress

The ability to assing a "modifier only double keypress" as a key binding.

ex:

"keys": ["control+control"] = Typing the control key twice-in-a-row executes the command.

This would be really handy for the Control Palette.

It's a nice way to get another "easy target" keyboard shortcut after all of the "space+___" shortcuts have been taken.

I first saw this feature in Quicksilver and it's very convenient.

Here's some related links and information:

http://geek.michaelgrace.org/2011/02/double-key-press-activation-state-machine-thingy/

http://rawsyntax.com/blog/quicksilver-secure-keyboard-entry-and-single-modified-activaction/