Add tasks for all the new languages

Task/History-variables/Swift/history-variables-1.swift

@@ -0,0 +1,11 @@
+var historyOfHistory = [Int]()
+var history:Int = 0 {
+    willSet {
+        historyOfHistory.append(history)
+    }
+}
+
+history = 2
+history = 3
+history = 4
+println(historyOfHistory)

Task/History-variables/Swift/history-variables-2.swift

@@ -0,0 +1,38 @@
+struct History <T> {
+
+    private var _history = [T]()
+    var history : [T] {
+        return _history
+    }
+
+    var now : T {
+        return history.last!
+    }
+
+    init(_ firstValue:T) {
+        _history = [firstValue]
+    }
+
+    mutating func set(newValue:T) {
+        _history.append(newValue)
+    }
+
+    mutating func undo() -> T {
+        guard _history.count > 1 else { return _history.first! }
+        _history.removeLast()
+        return _history.last!
+    }
+}
+
+var h = History("First")
+h.set("Next")
+h.set("Then")
+h.set("Finally")
+h.history   // output ["First", "Next", "Then", "Finally"]
+
+h.now       // outputs "Finally"
+h.undo()    // outputs "Then"
+h.undo()    // outputs "Next"
+h.undo()    // outputs "First"
+h.undo()    // outputs "First", since it can't roll back any further
+h.undo()    // outputs "First"