Add a method reverse_segment

[xvolks]

pub fn reverse_segment(&mut self, start: usize, count: usize) -> Result<(), &str>

Reverse a part of the list from start for count elements.

Example

# use cdll::CircularList;
let mut saying: CircularList<_> = "reverting is part of coding".chars().collect();
saying.reverse_segment(13, 4);
assert_eq!("reverting is trap of coding", saying.into_iter().collect::<String>())