Function LinkedList.insertBack
Appen value v to the end.
Returns
Pointer to added list element.
Example
LinkedList!int list;
scope(exit) list .free();
auto element = list .append(13);
assert(element .datum == 13);
assert(list .length == 1);
element = list .append(42);
assert(element .datum == 42);
assert(list .length == 2);