title: Dictionary with item limit
body: <p>I need to provide access to a Key/Value pair store that persists for all users across session.</p>
  
  <p>I could easily create a singleton for this, but for performance reasons I want to limit the size of the dictionary to 10000 items (or any performant number, as the object will persist indefinitely)</p>
  
  <p>Is there a form of dictionary where I can specify a limit to the number of objects stored, and when that limit is exceeded, remove the oldest entry?</p>