input: Write a class to modify the case of the string. The class should include methods to convert the string to uppercase, lowercase, and title case. The class should take a string as input in its constructor and have methods to return the modified string.
  assert StringCaseModifier("Hello World").to_upper() == "HELLO WORLD"
  assert StringCaseModifier("Hello World").to_lower() == "hello world"
  assert StringCaseModifier("Hello World").to_title() == "Hello World"
output: class StringCaseModifier:
      def __init__(self, input_string):
          self.input_string = input_string
  
      def to_upper(self):
          return self.input_string.upper()
  
      def to_lower(self):
          return self.input_string.lower()
  
      def to_title(self):
          return self.input_string.title()