Add tasks for all the new languages

Task/Middle-three-digits/Sidef/middle-three-digits.sidef

@@ -0,0 +1,16 @@
+func middle_three(n) {
+  var l = n.len;
+  if (l < 3) {
+    "#{n} is too short"
+  } elsif (l.is_even) {
+    "#{n} has an even number of digits"
+  } else {
+    "The three middle digits of #{n} are: " + n.digits.ft(l-3 / 2, l/2 + 1).join
+  }
+}
+
+var nums = %n(
+    123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345
+    1 2 -1 -10 2002 -2002 0
+);
+nums.each { say middle_three(_) };