title: How to load XML document from `std::istream`?
body: <p>I'd like to load TinyXml documents from <code>std::istream</code>, but it doesn't contain such method:</p>
  
  <pre><code>/** Load a file using the current document value.
      Returns true if successful. Will delete any existing
      document data before loading.
  */
  bool LoadFile( TiXmlEncoding encoding = TIXML_DEFAULT_ENCODING );
  /// Save a file using the current document value. Returns true if successful.
  bool SaveFile() const;
  /// Load a file using the given filename. Returns true if successful.
  bool LoadFile( const char * filename, TiXmlEncoding encoding = TIXML_DEFAULT_ENCODING );
  /// Save a file using the given filename. Returns true if successful.
  bool SaveFile( const char * filename ) const;
  /** Load a file using the given FILE*. Returns true if successful. Note that this method
      doesn't stream - the entire object pointed at by the FILE*
      will be interpreted as an XML file. TinyXML doesn't stream in XML from the current
      file location. Streaming may be added in the future.
  */
  bool LoadFile( FILE*, TiXmlEncoding encoding = TIXML_DEFAULT_ENCODING );
  </code></pre>
  
  <p>I see that it contains function that uses <code>FILE</code>, is it possible to convert <code>std::istream</code> to <code>FILE</code>?</p>