Add tasks for all the new languages

Task/Substring-Top-and-tail/Swift/substring-top-and-tail-1.swift

@@ -0,0 +1,4 @@
+let txt = "0123456789"
+println(dropFirst(txt))
+println(dropLast(txt))
+println(dropFirst(dropLast(txt)))

Task/Substring-Top-and-tail/Swift/substring-top-and-tail-2.swift

@@ -0,0 +1,4 @@
+let txt = "0123456789"
+println(txt[txt.startIndex.successor() ..< txt.endIndex])
+println(txt[txt.startIndex             ..< txt.endIndex.predecessor()])
+println(txt[txt.startIndex.successor() ..< txt.endIndex.predecessor()])

Task/Substring-Top-and-tail/Swift/substring-top-and-tail-3.swift

@@ -0,0 +1,3 @@
+var txt = "0123456789"
+txt.removeAtIndex(txt.startIndex)
+txt.removeAtIndex(txt.endIndex.predecessor())

Task/Substring-Top-and-tail/Swift/substring-top-and-tail-4.swift

@@ -0,0 +1,55 @@
+extension String {
+
+    /// Ensure positive indexes
+
+    private func positive(index: Int) -> Int {
+
+        if index >= 0 { return index }
+
+        return count(self) + index
+    }
+
+    /// Unicode character by zero-based integer (character) `index`
+    /// Supports negative character index to count from end. (-1 returns character before last)
+
+    subscript(index: Int) -> Character {
+
+        return self[advance(startIndex, positive(index))]
+    }
+
+    /// String slice by character index
+
+    subscript(range: Range<Int>) -> String {
+
+        return self[advance(startIndex, range.startIndex) ..<
+                    advance(startIndex, range.endIndex, endIndex)]
+    }
+
+    /// Left portion of text to `index`
+
+    func left(index : Int) -> String {
+
+        return self[0 ..< positive(index)]
+    }
+
+    /// Right portion of text from `index`
+
+    func right(index : Int) -> String{
+
+        return self[positive(index) ..< count(self)]
+    }
+
+    /// From `start` index until `end` index
+
+    func mid(start: Int, _ end: Int) -> String {
+
+        return self[positive(start) ..< positive(end)]
+    }
+
+}
+
+let txt = "0123456789"
+
+txt.right(1) // Right part without first character
+txt.left(-1) // Left part without last character
+txt.mid(1,-1) // Middle part without first and last character