Add tasks for all the new languages

Task/Symmetric-difference/Ring/symmetric-difference.ring

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+alist = []
+blist = []
+alist = ["john", "bob", "mary", "serena"]
+blist = ["jim", "mary", "john", "bob"]
+
+alist2 = []
+for i = 1 to len(alist)
+    flag = 0
+    for j = 1 to len(blist)
+        if alist[i] = blist[j]  flag = 1 ok
+    next
+    if (flag = 0) add(alist2, alist[i]) ok
+next
+
+blist2 = []
+for j = 1 to len(alist)
+    flag = 0
+    for i = 1 to len(blist)
+        if alist[i] = blist[j]  flag = 1 ok
+    next
+    if (flag = 0) add(blist2, blist[j]) ok
+next
+see "a xor b :" see nl
+see alist2
+see blist2 see nl
+see "a-b :" see nl
+see alist2 see nl
+see "b-a :" see nl
+see blist2 see nl