Add a USE_PLUGINS() macro

The `USE_PLUGINS()` macro is a clever hack, to make it seem like
`Kaleidoscope.use()` is type-safe. It pushes its arguments into an appropriately
typed array, so anything that does not fit the criteria, will trigger a compiler
error.

It then never uses the array, and passes the plugins over to
`Kaleidoscope.use`, adding the trailing `NULL`, making it even easier to
use.

Since the array this macro creates is never used, the compiler will
optimize it out fully. As such, by using this macro, we incur neither
any size penalties, nor any run-time penalties. Everything happens at
compile-time.

Fixes #100.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

src/Kaleidoscope.h

@@ -34,6 +34,24 @@ extern HARDWARE_IMPLEMENTATION KeyboardHardware;
 
 #define KEYMAP_SIZE (sizeof(keymaps) / ROWS / COLS / sizeof(Key))
 
+/*
+ * The `USE_PLUGINS()` macro is a clever hack, to make it seem like
+ * `Kaleidoscope.use()` is type-safe. It pushes its arguments into an
+ * appropriately typed array, so anything that does not fit the criteria, will
+ * trigger a compiler error.
+ *
+ * It then never uses the array, and passes the plugins over to
+ * `Kaleidoscope.use`, adding the trailing `NULL`, making it even easier to use.
+ *
+ * Since the array this macro creates is never used, the compiler will optimize
+ * it out fully. As such, by using this macro, we incur neither any size
+ * penalties, nor any run-time penalties. Everything happens at compile-time.
+ */
+#define USE_PLUGINS(plugins...) ({                              \
+          static KaleidoscopePlugin *__p[] = {plugins, NULL};   \
+          Kaleidoscope.use(plugins, NULL);                      \
+        })
+
 class KaleidoscopePlugin {
  public:
   virtual void begin(void) = 0;