pub fn push_back(&mut self, elt: T) {
        self.push_back_node(box Node::new(elt));
    }
Removes the element at the given index and returns it.

This operation should compute in *O*(*n*) time.

# Panics
Panics if at >= len

# Examples

```
#![feature(linked_list_remove)]
use std::collections::Linked
benchmarks/haystacks/code/rust-library.rs