reset modifier when entering OFF state

USB power allows the modifier variable to persist. The power is cut
when entering OFF on battery, so emulate this behavior by resetting
the modifier.
invert activation from button down to button up

Modifiers based on long button presses have a better feel if the basic
activation is on button up.
make: follow changes in config.h
set long down to 1/2 second
oops: only compile .c files
ignore object files
only switch states on short button press

Long button presses now only modify the mode and don't cause a
light state change.
re-fix power-off when usb is disconnected
long button down only when on

If we have a long-down when OFF, then we should just switch on.