Added EPHEMERAL keyswitch state flag

An `EPHEMERAL` keyswitch event is one that gets ignored by updates to
`live_composite_keymap_[]`, and thus doesn't change the keymap at all. This is useful for
a plugin that needs to retain its own key type in the keymap in order to do something
particular when it toggles off, but needs to inject an event with a different `Key` value,
with real key coordinates.

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

src/kaleidoscope/key_events.cpp

@@ -82,7 +82,7 @@ void handleKeyswitchEvent(Key mappedKey, byte row, byte col, uint8_t keyState) {
     /* If a key had an on event, we update the live composite keymap. See
      * layers.h for an explanation about the different caches we have. */
     if (keyToggledOn(keyState)) {
-      if (mappedKey.raw == Key_NoKey.raw) {
+      if (mappedKey.raw == Key_NoKey.raw || keyState & EPHEMERAL) {
         Layer.updateLiveCompositeKeymap(row, col);
       } else {
         Layer.updateLiveCompositeKeymap(row, col, mappedKey);

src/kaleidoscope/keyswitch_state.h

@@ -20,6 +20,7 @@
 #include <Arduino.h>
 
 #define INJECTED    B10000000
+#define EPHEMERAL   B01000000
 #define IS_PRESSED  B00000010
 #define WAS_PRESSED B00000001