input: Write a python function to manage a min-heap by adding and popping elements.
  assert create_heap([4, 5, 2, 33, 1])==None
  assert add_item([1, 4, 2, 33, 5], 6)==None
  assert pop_item([1, 4, 2, 33, 5, 6])==1
output: import heapq
  
  def create_heap(arr):
      heapq.heapify(arr)
  
  def add_item(heap, item):
      heapq.heappush(heap, item)
  
  def pop_item(heap):
      return heapq.heappop(heap)