Make perspective scale work more explicitly from properties

include/akgl/tilemap.h

@@ -91,6 +91,8 @@ typedef struct {
     int p_vanishing_y;
     int p_foreground_h;
     int p_vanishing_h;
+    float p_foreground_scale;
+    float p_vanishing_scale;
     float p_scale;
     float p_rate;
     akgl_Tileset tilesets[AKGL_TILEMAP_MAX_TILESETS];