Add tasks for all the new languages

Task/Mutual-recursion/Ceylon/mutual-recursion.ceylon

@@ -0,0 +1,14 @@
+Integer f(Integer n)
+    =>  if (n > 0)
+        then n - m(f(n-1))
+        else 1;
+
+Integer m(Integer n)
+    =>  if (n > 0)
+        then n - f(m(n-1))
+        else 0;
+
+shared void run() {
+    printAll((0:20).map(f));
+    printAll((0:20).map(m));
+}