/// <summary>
/// Returns a page worth of items from the specified collection.
/// </summary>
/// <typeparam name="TSource">the type of the items in the collection</typeparam>
/// <param name="source">an IEnumerable&gt;TSource&lt; of items to page</param>
/// <param name="pageNumber">the number of the page to return</param>
/// <param name="itemsPerPage">the number of items that make up a page</param>
/// <returns>
/// An IEnumerable&gt;TSource&lt; the contains the specified number of items for the specified pageNumber. 
/// If pageNumber exceeds the number of available pages, the returned collection will be empty.