Add tasks for all the new languages

Task/Variadic-function/XLISP/variadic-function.xlisp

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+(defun print-on-separate-lines (&rest xs)
+    (for-each print xs))
+
+; test the function:
+
+(print-on-separate-lines 'i 'am 'doing 'a 'great 'work 'so 'that 'i 'cannot 'come 'down)
+
+; to use it on a list of arguments assembled at run time, first create your list
+
+(define test '(why should the work cease whilst i leave it and come down to you))
+
+; and then call APPLY:
+
+(apply print-on-separate-lines test)