move documentation markdown to system directory.

laravel/documentation/session/usage.md

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+# Session Usage
+
+## Contents
+
+- [Storing Items](#put)
+- [Retrieving Items](#get)
+- [Removing Items](#forget)
+- [Regeneration](#regeneration)
+
+<a name="put"></a>
+## Storing Items
+
+To store items in the session call the put method on the Session class:
+
+	Session::put('name', 'Taylor');
+
+The first parameter is the **key** to the session item. You will use this key to retrieve the item from the session. The second parameter is the **value** of the item.
+
+The **flash** method stores an item in the session that will expire after the next request. It's useful for storing temporary data like status or error messages:
+
+	Session::flash('status', 'Welcome Back!');
+
+<a name="get"></a>
+## Retrieving Items
+
+You can use the **get** method on the Session class to retrieve any item in the session, including flash data. Just pass the key of the item you wish to retrieve:
+
+	$name = Session::get('name');
+
+By default, NULL will be returned if the session item does not exist. However, you may pass a default value as a second parameter to the get method:
+
+	$name = Session::get('name', 'Fred');
+
+	$name = Session::get('name', function() {return 'Fred';});
+
+Now, "Fred" will be returned if the "name" item does not exist in the session.
+
+Laravel even provides a simple way to determine if a session item exists using the **has** method:
+
+	if (Session::has('name'))
+	{
+	     $name = Session::get('name');
+	}
+
+<a name="forget"></a>
+## Removing Items
+
+To remove an item from the session use the **forget** method on the Session class:
+
+	Session::forget('name');
+
+You can even remove all of the items from the session using the **flush** method:
+
+	Session::flush();
+
+<a name="regeneration"></a>
+## Regeneration
+
+Sometimes you may want to "regenerate" the session ID. This simply means that a new, random session ID will be assigned to the session. Here's how to do it:
+
+	Session::regenerate();