Initial implementation of ReignEngine HLL

ReignEngine is the 3D rendering engine used in Toushin Toshi III, and is
the predecessor of the 3D engines for Rance Quest, Rance 9, Evenicle,
etc.

This implements minimal functionality to be able to draw the first 3D
dungeon scene. Many important parts such as motion and lighting are not
implemented yet.

include/plugin.h

@@ -17,9 +17,11 @@
 #ifndef SYSTEM4_PLUGIN_H
 #define SYSTEM4_PLUGIN_H
 
+struct sact_sprite;
+
 struct draw_plugin {
 	const char *name;
-	void (*update)(struct draw_plugin *);
+	void (*update)(struct sact_sprite *);
 };
 
 #endif /* SYSTEM4_PLUGIN_H */