Add tasks for all the new languages

Task/Rot-13/Sidef/rot-13.sidef

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+# Returns a copy of 's' with rot13 encoding.
+func rot13(s) {
+    s.tr('A-Za-z', 'N-ZA-Mn-za-m');
+}
+
+# Perform rot13 on standard input.
+STDIN.each { |line| print rot13(line) }