input: Write a function that implements a hash table in Python that supports insert, delete and retrieve operations. If the given key does not exist during retrieve or delete operations, return None.
  assert hash_table_insert_retrieve(HashTable, 'key1', 'value1')==True
  assert hash_table_insert_retrieve(HashTable, 'key1', 'value2')==True
  assert hash_table_retrieve(HashTable, 'key1')=='value2'
  assert hash_table_delete(HashTable, 'key1')==None
  assert hash_table_retrieve(HashTable, 'key1')==None
output: def hash_table_insert_retrieve(self, key, value):
      self.table[key] = value
      return self.table[key] == value
  
  def hash_table_retrieve(self, key):
      return self.table.get(key, None)
  
  def hash_table_delete(self, key):
      if key in self.table:
          del self.table[key]
      return None