allow hiding bg layers; hide it in tutorial

vacation.p8

@@ -907,8 +907,8 @@ end
 function zonk_mode:draw()
  cls(0)
  pal(self.p, 1)
- self.stripes:draw()
- self.brth:draw()
+ if (not self.hide_stripes) self.stripes:draw()
+ if (not self.hide_breath) self.brth:draw()
  if self.fpfrm then
   local ffrac = self.fpfrm/self.exf
   fadetbl(12, self.fd12, ffrac)
@@ -1674,6 +1674,7 @@ BE A TUTORIAL HERE.]],
     txd=0,
     txf=1,
     cmul=0.25,
+    hide_stripes=true,
    }},
   },
   {