title: boost::program_options config file format
body: <p>I am using boost::program_options to load command line arguments. Now I want to additionally load a config file with the same arguments set. I use it in very standard way:</p>
  
  <pre><code>ifstream ifs(filename.c_str());
  if (ifs) {
      po::store(po::parse_config_file(ifs, optionsDescription), vm);
      po::notify(vm);
  }
  </code></pre>
  
  <p>The thing is that parse_config_file accepts ini files in following standard format:</p>
  
  <pre><code>key1=value
  key2 = value
  </code></pre>
  
  <p>But my file does not use "equal sign" to separate key and value but only spaces and/or tabs like this:</p>
  
  <pre><code>key1 value
  key2  value
  </code></pre>
  
  <p>I need to keep this format for compatibility reason. Is there any way to achieve this with boost program_options?
  I have found style option of command_line parses, but there seems to be nothing like that for parse_config_file.</p>