Add window-swicher.py

alt-shift-digit to save current foreground window
then ctrl-alt-digit to bring it back
Fix ctrl-alt break ctrl's down state bug

When ctrl down, alt down, ctrl up, alt up
the 'ctrl up' will be modified by `alt` so to generate
WM_SYSKEYUP event, so using only WM_KEYUP will miss that
Fix to not rely on manual log the up/down state,
instead, use GetKeyState()