code: function createCommand(fn) {
    assert.ok(fn.name, 'commands must be named functions');
  
    git[fn.name] = decorator.bind(null, fn);
    return git;
  }
docs: Creates a {@link command} in this module.
  Third party developers must use it to create their owns
  parameters
  
  @memberof git
  @alias command
  @param {command} fn The named function implementing a command
  @returns {Function} function The gitftw module, for chainability