input: Write a python function to convert temperature from Fahrenheit to Celsius, Celsius to Kelvin, and Kelvin to Fahrenheit using a Temperature class.
  assert Temperature(32, 'F').convert_to_celsius() == 0
  assert Temperature(0, 'C').convert_to_celsius() == 0
  assert Temperature(273.15, 'K').convert_to_celsius() == 0
output: class Temperature:
      def __init__(self, value, unit):
          self.value = value
          self.unit = unit
  
      def convert_to_celsius(self):
          if self.unit == 'F':
              return (self.value - 32) * 5 / 9
          elif self.unit == 'C':
              return self.value
          elif self.unit == 'K':
              return self.value - 273.15
  
      def convert_to_kelvin(self):
          if self.unit == 'F':
              return (self.value - 32) * 5 / 9 + 273.15
          elif self.unit == 'C':
              return self.value + 273.15
          elif self.unit == 'K':
              return self.value
  
      def convert_to_fahrenheit(self):
          if self.unit == 'F':
              return self.value
          elif self.unit == 'C':
              return (self.value * 9 / 5) + 32
          elif self.unit == 'K':
              return (self.value - 273.15) * 9 / 5 + 32