Add tasks for all the new languages

Task/Mutual-recursion/Phix/mutual-recursion-1.phix

@@ -0,0 +1,15 @@
+function F(integer n)
+    return iff(n?n-M(F(n-1)):1)
+end function
+
+function M(integer n)
+    return iff(n?n-F(M(n-1)):0)
+end function
+
+for i=0 to 20 do
+    printf(1," %d",F(i))
+end for
+printf(1,"\n")
+for i=0 to 20 do
+    printf(1," %d",M(i))
+end for

Task/Mutual-recursion/Phix/mutual-recursion-2.phix

@@ -0,0 +1,2 @@
+forward function F(integer n)
+forward function M(integer n)