implement a function slice_link that slices a given link. slice_link should slice the link starting at start and ending one element before end, as with a normal python list.
def slice_link(link, start, end):
"""Slices a Link from start to end (as with a normal Python list).
>>> link = Link(3, Link(1, Link(4, Link(1, Link(5, Link(9))))))
>>> new = slice_link(link, 1, 4)
>>> new
Link(1, Link(4, Link(1)))
>>> link2 = slice_link(Link(1), 0, 1)
>>> link2
Link(1)
>>> link3 = slice_link(Link.empty, 0, 0)
>>> link3
()
"""
"*** YOUR CODE HERE ***"