Modifier key sends Esc

Modifier key sends Esc

Adds possibility to make the left Ctrl, Alt, or Cmd key function as a
second Esc key.  The key will still function as a modifier if held down
in conjunction with another key.  Enable by setting the user default
"MMFakeEscModifier" to:
    1 = Left Ctrl
    2 = Left Alt
    3 = Left Cmd
    any other number disables this functionality

By remapping Caps-Lock to one of the above modifier keys this enables
the use of Caps-Lock as a second (and easy to reach) Esc key.  Caps-Lock
can be remapped inside "System Preferences -> Keyboard & Mouse ->
Modifier Keys...".

The Esc event is sent when the modifier key is released.  If the key is
not released within a predefined timeout, then no Esc event is
generated.  The timeout can be changed by setting the user default
MMFakeEscTimeout (a float, specifying the timeout in seconds).

The fact that the Esc event is sent on release makes it feel somewhat
sluggish.  It is possible to have the event sent when the modifier key
is pressed by setting the user default "MMFakeEscOnKeyDown" but then the
left modifier key can only be used as an Esc key.