Add tasks for all the new languages

Task/Null-object/Swift/null-object-1.swift

@@ -0,0 +1,2 @@
+var opt : Int? = nil // use "nil" to represent no value
+opt = 5 // or simply assign a value to the optional type

Task/Null-object/Swift/null-object-2.swift

@@ -0,0 +1,5 @@
+if let v = opt {
+    println("There is some value: \(v)")
+} else {
+    println("There is no value")
+}