can be an element that is implicitly convertible to T, an input range of such elements, or another singly linked list
the newly created list
Complexity: O(n + m), where m is the number of elements in rhs.
import std.algorithm.comparison : equal; auto sl = SList!int(1); auto sl2 = sl ~ 2; assert(equal(sl2, [1, 2])); sl.front = 0; assert(equal(sl2, [1, 2]));
Create a new list that results from the concatenation of this list with rhs.