Add tasks for all the new languages

Task/Singly-linked-list-Traversal/Nim/singly-linked-list-traversal.nim

@@ -0,0 +1,26 @@
+type Node[T] = ref object
+  next: Node[T]
+  data: T
+
+proc newNode[T](data: T): Node[T] =
+  Node[T](data: data)
+
+var a = newNode 12
+var b = newNode 13
+var c = newNode 14
+
+proc insertAppend(a, n: var Node) =
+  n.next = a.next
+  a.next = n
+
+a.insertAppend(b)
+b.insertAppend(c)
+
+iterator items(a: Node) =
+  var x = a
+  while x != nil:
+    yield x
+    x = x.next
+
+for item in a:
+  echo item.data