code: function headers( opts ) {
  	var out = {};
  	if ( opts.useragent ) {
  		debug( 'User-Agent: %s', opts.useragent );
  		out[ 'User-Agent' ] = opts.useragent;
  	}
  	if ( opts.accept ) {
  		debug( 'Accept: %s', opts.accept );
  		out[ 'Accept' ] = opts.accept;
  	}
  	if ( opts.token ) {
  		out[ 'Authorization' ] = 'token ' + opts.token;
  	}
  	return out;
  }
docs: HEADERS // 
  FUNCTION: headers( opts )
  Returns request headers based on provided options.
  
  @param {Object} opts - provided options
  @param {String} [opts.token] - Github access token
  @param {String} [opts.accept] - media type
  @param {String} [opts.useragent] - user agent string
  @returns {Object} request headers