Add support for Apple's m4b/m4a formats

The description for this software says "It is primarily intended for accelerating audio books and podcasts...". Then it should support Apple's audio book format .m4b. One can use mp3 for audio books, and that works fairly well on other devices, but not so well on Apple's. While uploading mp3 files to an iPod/iPhone/iPad they will appear under music. To make them appear under Audio Books one need to upload .m4b files. Playing audio books as audio books, and not as music gives bookmarks, so you can resume playback where you stopped listening the previous time. W mp3 files you will have to remember which file you were at, and restart from the beginning of that file. Playback of long mp3 files seams to cut the track after a few minutes, skipping to next track, which might be okey for music, but it renders audio books useless. Playback of mp3 files might be done shuffled, unless you remembered to turn off shuffling. This is very annoying after listening to a book for a few minutes, realizing you jumped from chapter one to chapter nine and then back to chapter 4. All this is easily solved by using the audio book format .m4b, so there are good reasons to support it.