code: function createShell(config, callback) {
    var shell = new Shell(config);
  
    modules.initialize(shell);
    extensions.initialize(shell);
  
    require('./commands').initialize(shell);
    require('./displayCommands').initialize(shell);
    require('./dataCommands').initialize(shell);
  
    process.nextTick(function() {
      callback(shell);
    });
  }
docs: Creates and initializes a Shell object.