/*
 * Add one or more songs to the playlist.
 *
 * Examples:
 *   # replace the current playlist with one song
 *   enqueue = false
 *   remote.add 'path/to/cool_song.mp3', enqueue
 *
 *   # add several files to the current playlist
 *   files = %w{song01.mp3 song02.mp3 song03.mp3 song04.mp3 song05.mp3}
 *   remote.add *files
 *
 */
static VALUE xr_pl_add(int argc, VALUE *argv, VALUE self) {