Deprecate USE_PLUGINS

`Kaleidoscope.use` is a much better interface, therefore deprecate USE_PLUGINS.
We do this by creating a wrapper function, `__USE_PLUGINS` that will call
`Kaleidoscope.use` under the hood, but has a deprecated attribute attached. We
then make the `USE_PLUGINS` macro call this function.

We do this because we want to make sure that the list is NULL-terminated, and
for that, we need the macro.

Signed-off-by: Gergely Nagy <kaleidoscope@gergo.csillger.hu>

src/Kaleidoscope.cpp

@@ -144,3 +144,14 @@ void event_handler_hook_use(Kaleidoscope_::eventHandlerHook hook) {
 void loop_hook_use(Kaleidoscope_::loopHook hook) {
   Kaleidoscope.useLoopHook(hook);
 }
+
+void __USE_PLUGINS(KaleidoscopePlugin *plugin, ...) {
+  va_list ap;
+
+  Kaleidoscope.use(plugin);
+
+  va_start(ap, plugin);
+  while ((plugin = (KaleidoscopePlugin *)va_arg(ap, KaleidoscopePlugin *)) != NULL)
+    Kaleidoscope.use(plugin);
+  va_end(ap);
+}

src/Kaleidoscope.h

@@ -36,8 +36,6 @@ extern HARDWARE_IMPLEMENTATION KeyboardHardware;
 const uint8_t KEYMAP_SIZE
 __attribute__((deprecated("Kaleidoscope.setup() does not require KEYMAP_SIZE anymore."))) = 0;
 
-#define USE_PLUGINS(plugins...) Kaleidoscope.use(plugins)
-
 class KaleidoscopePlugin {
  public:
   virtual void begin(void) = 0;
@@ -122,7 +120,13 @@ extern Kaleidoscope_ Kaleidoscope;
                                            "layer.getState")
 
 /* -- DEPRECATED aliases; remove them when there are no more users. -- */
+
 void event_handler_hook_use(Kaleidoscope_::eventHandlerHook hook)
 __attribute__((deprecated("Use Kaleidoscope.useEventHandlerHook instead")));
 void loop_hook_use(Kaleidoscope_::loopHook hook)
 __attribute__((deprecated("Use Kaleidoscope.useLoopHook instead")));
+
+void __USE_PLUGINS(KaleidoscopePlugin *plugin, ...)
+__attribute__((deprecated("Use Kaleidoscope.use(...) instead")));
+
+#define USE_PLUGINS(...) __USE_PLUGINS(__VA_ARGS__, NULL)