detach pause screen from camera (fixes #36)

game.gd

@@ -152,4 +152,4 @@ func _process(delta):
 		#Pause
 		if Input.is_action_just_pressed("pause"):
 			var viewport = get_parent().get_node("Main/Control/ViewportContainer/Viewport")
-			instance_node(pause_screen,0,0,viewport)
+			viewport.add_child(pause_screen.instance())

objects/hud/pause_screen.gd

@@ -1,4 +1,4 @@
-extends Node2D
+extends CanvasLayer
 
 # Called when the node enters the scene tree for the first time.
 func _ready():

objects/hud/pause_screen.tscn

@@ -5,8 +5,9 @@
 [ext_resource path="res://graphics/hud/pause_arrow.png" type="Texture" id=3]
 [ext_resource path="res://objects/hud/pause_screen.gd" type="Script" id=4]
 
-[node name="PauseScreen" type="Node2D"]
+[node name="PauseScreen" type="CanvasLayer"]
 pause_mode = 2
+layer = 100
 script = ExtResource( 4 )
 
 [node name="TileMap" type="TileMap" parent="."]