Optimized Lists. Added pool.added and .removed. Added entity:ensure

lib/pool.lua

@@ -14,6 +14,9 @@ Pool.__index = Pool
 function Pool.new(name, filter)
    local pool = setmetatable(List(), Pool)
 
+   pool.added   = {}
+   pool.removed = {}
+
    pool.name   = name
    pool.filter = filter
 
@@ -22,6 +25,12 @@ function Pool.new(name, filter)
    return pool
 end
 
+function Pool:flush()
+   for i = 1, math.max(#self.added, #self.removed) do
+      self.added[i], self.removed[i] = nil, nil
+   end
+end
+
 --- Checks if an Entity is eligible for the Pool.
 -- @param e The Entity to check
 -- @return True if the entity is eligible, false otherwise