title: Boost bimap find with multiset_of
body: <p>I have question with Boost::bimap and could not find answer from boost document.</p>
  
  <pre><code>using AToBBimap = boost::bimap&lt; boost::bimaps::unordered_set_of&lt;CString&gt;, boost::bimaps::multiset_of&lt;CString&gt; &gt;; //hashed bimap
  using AToBBimapValueT = AToBBimap ::value_type;
  
  AToBBimap bi_map;
  bi_map.insert(AToBBimapValueT{"message1", "value"});
  bi_map.insert(AToBBimapValueT{"message2", "value"});
  
  bi_map.right.find("value");
  </code></pre>
  
  <p>QUESTION: with <code>bi_map.right.find("value")</code> looks like can only get iterator to <code>{"message1", "value"}</code>, is there possible to get a list of both matching like <code>[{"message1", "value"}, {"message2", "value"}]</code>?</p>