Time-stretching audio can't be turned off

Turning off the "Time-strectching audio" option in the settings doesn't actually turn it off, the time-stretching is still present.

I think I found the problem: the audio-time-stretch option is set using the addOptions method, which calls libvlc's libvlc_media_add_option method. On that method's description, it's noted that most audio options have no effect, and they should be set during the initialization of the libvlc instance.

Here's an example that I've done that seems to work (although I don't have any Objective-C experience, thus this is not a PR) on the startPlayback method in VLCPlaybackService.m

BOOL audioTimeStretching = [[userDefaults objectForKey:kVLCSettingStretchAudio] boolValue];

if (!audioTimeStretching)
    [libVLCOptions addObject:[@"--no-" stringByAppendingString:kVLCSettingStretchAudio]];