feat: add esc_current_scene reserved global (#474)

Co-authored-by: Duncan Brown <duncan@bhs-consultants.com>

game/rooms/room16/esc/current_scene_button.esc

@@ -0,0 +1,11 @@
+:use
+
+> [eq ESC_CURRENT_SCENE room16]
+	say player "This sure looks like room 16."
+	
+> [eq ESC_CURRENT_SCENE ESC_LAST_SCENE]
+	say player "I'll never say this."
+
+> [eq ESC_CURRENT_SCENE room1]
+	say player "I'll never say this, either."
+

game/rooms/room16/esc/left_exit.esc

@@ -0,0 +1,3 @@
+:exit_scene
+play_snd res://game/sfx/sounds/doorOpen_2.ogg
+change_scene "res://game/rooms/room15/room15.tscn"

game/rooms/room16/esc/room16.esc

@@ -0,0 +1,8 @@
+:setup
+
+> [eq ESC_LAST_SCENE room15]
+	teleport player r16_l_exit
+	# Set player look right
+	set_angle player 90
+	stop
+