Refactor collider to collaborate with linked_list.

The only use of a collider is intertwined with the ship list, so I can combine the "prepare to yoink" and "populate collider" and "iterate list" steps, and I can combine the "hide" and "yoink" steps. This doesn't save tokens now but it's about to, when I use the eship collider to test pship collision.

vacuum_gambit.p8

@@ -259,28 +259,11 @@ function updategame()
 
 	-- many bullets and many enemy ships;
 	-- use bucket collider for efficiency
+ local eship_collider = collider.new{from=eships}
 
- local eship_collider, pp = collider.new(), eships
- eships:strip(function(s)
-  eship_collider:insert(s)
-  s.prev = pp
-  pp = s
-end)
-
- -- lose tokens, save time:
- -- unroll `strip` to avoid
- -- function call overhead
  pbullets:strip(function(pb)
   for es in all(eship_collider:get_collisions(pb)) do
-   if es:hitbullet(pb) then
+   if (es:hitbullet(pb)) eship_collider:yoink(es)
-    eship_collider:hide(es)
-    es.prev.next=es.next
-    if es.next then
-     es.next.prev = es.prev
-    else
-     eships.tail = es.prev
-    end
-   end
    if (pb:hitship(es)) return true
   end
  end)
@@ -1446,6 +1429,21 @@ end
 collider = mknew{
  init = function(x)
   x.suppress = {}
+  local p, n = x.from, x.from.next
+  while n do
+   -- insert
+   for i in all(collider_indexes(hurtbox(n))) do
+    local a = x[i]
+    if not a then
+     a = {}
+     x[i] = a
+    end
+    add(a, n)
+   end
+   -- prepare yoink
+   n.prev = p
+   p = n
+  end
  end,
 }
 
@@ -1459,21 +1457,15 @@ function collider_indexes(box)
  return ret
 end
 
-function collider:insert(item)
+function collider:yoink(item)
- -- todo: separate "big items" list?
- local bdx = collider_indexes(hurtbox(item))
- for i in all(bdx) do
-  local x = self[i]
-  if not x then
-   x = {}
-   self[i] = x
-  end
-  add(x, item)
- end
-end
-
-function collider:hide(item)
  self.suppress[item]=true
+ local p,n = item.prev,item.next
+ p.next = n
+ if n then
+  n.prev = p
+ else
+  self.from.tail = p
+ end
 end
 
 function collider:get_collisions(item)