input: Write a python function to call multiple functions in a sequence.
  assert greetings() is None
output: def call_in_sequence(*functions):
      for function in functions:
          function()
  
  def greetings():
      def say_hello():
          print("Hello")
      
      def ask_how_are_you():
          print("How are you?")
      
      def say_goodbye():
          print("Goodbye")
      
      call_in_sequence(say_hello, ask_how_are_you, say_goodbye)