Added Markdown Documentation to Stack playground

This might be overkill for such a small file, but I wish I started using Swift Markdown early in my iOS career.  Option click is too convenient to ignore!

Author: alextakahashi

Stack/Stack.playground/Contents.swift

@@ -1,4 +1,4 @@
-/*
+/**
   Stack
 
   A stack is like an array but with limited functionality. You can only push
@@ -9,27 +9,51 @@
   last is the first one to come off with the next pop.
 
   Push and pop are O(1) operations.
+ 
+  ## Usage
+  ```
+  var myStack = Stack(array: [])
+  myStack.push(10)
+  myStack.push(3)
+  myStack.push(57)
+  myStack.pop() // 57
+  myStack.pop() // 3
+ ```
 */
-
 public struct Stack<T> {
+    
+  /// Datastructure consisting of a generic item.
   fileprivate var array = [T]()
 
+  /// The number of items in the stack.
   public var count: Int {
     return array.count
   }
 
+  /// Verifies if the stack is empty.
   public var isEmpty: Bool {
     return array.isEmpty
   }
 
+  /**
+     Pushes an item to the top of the stack.
+     
+     - Parameter element: The item being pushed.
+  */
   public mutating func push(_ element: T) {
     array.append(element)
   }
 
+  /**
+     Removes and returns the item at the top of the sack.
+     
+     - Returns: The item at the top of the stack.
+  */
   public mutating func pop() -> T? {
     return array.popLast()
   }
 
+  /// Returns the item at the top of the stack.
   public var top: T? {
     return array.last
   }