Add tasks for all the new languages

Task/Sorting-algorithms-Shell-sort/Sidef/sorting-algorithms-shell-sort.sidef

@@ -0,0 +1,18 @@
+func shell_sort(a) {
+    var h = a.len;
+    while (h >>= 1) {
+        for i in (h .. a.end) {
+            var k = a[i];
+            for (var j = i; (j >= h) && (k < a[j - h]); j -= h) {
+                a[j] = a[j - h];
+            }
+            a[j] = k;
+        }
+    }
+    return a;
+}
+
+var a = 10.of {100.irand};
+say a;
+shell_sort(a);
+say a;