input: Write a function to perform string slicing in Python that takes a string, a start index, and an end index, and returns the sliced portion of the string. The function should be named slicing.
  assert slicing("This is a slicing test", 8, 15)=="a slicing"
  assert slicing("Hello World!", 6, 11)=="World"
  assert slicing("Python is awesome", 7, 10)=="is"
  assert slicing("Quick brown fox", 0, 5)=="Quick"
  assert slicing("", 0, 0)==""
output: def slicing(s, start, end):
      return s[start:end]