Add tasks for all the new languages

Task/Higher-order-functions/Lily/higher-order-functions.lily

@@ -0,0 +1,26 @@
+define square(x: Integer): Integer
+{
+    return x * x
+}
+
+var l = [1, 2, 3] # Inferred type: List[Integer].
+
+# Transform using a user-defined function.
+print(l.map(square)) # [1, 4, 9]
+
+# Using a built-in method this time.
+print(l.map(Integer.to_s)) # ["1", "2", "3"]
+
+# Using a lambda (with the type of 'x' properly inferred).
+print(l.map{|x| (x + 1).to_s()}) # ["2", "3", "4"]
+
+# In reverse order using F#-styled pipes.
+Boolean.to_i |> [true, false].map |> print
+
+define apply[A, B](value: A, f: Function(A => B)): B
+{
+    return f(value)
+}
+
+# Calling user-defined transformation.
+print(apply("123", String.parse_i)) # Some(123)