Add tasks for all the new languages

Task/Sorting-algorithms-Shell-sort/Swift/sorting-algorithms-shell-sort.swift

@@ -0,0 +1,17 @@
+func shellsort<T where T : Comparable>(inout seq: [T]) {
+    var inc = seq.count / 2
+    while inc > 0 {
+        for (var i, el) in EnumerateSequence(seq) {
+            while i >= inc && seq[i - inc] > el {
+                seq[i] = seq[i - inc]
+                i -= inc
+            }
+            seq[i] = el
+        }
+        if inc == 2 {
+            inc = 1
+        } else {
+            inc = inc * 5 / 11
+        }
+    }
+}