Add skeleton architecture for displaying custom splash screen

fusee/fusee-secondary/src/splash_screen.h

@@ -0,0 +1,9 @@
+#ifndef FUSEE_SPLASH_SCREEN_H
+#define FUSEE_SPLASH_SCREEN_H
+
+/* TODO: Actually make this a real thing. */
+extern unsigned char g_default_splash_screen[1];
+
+void display_splash_screen_bmp(const char *custom_splash_path);
+
+#endif