Add adelay filter

[Xcodo]

I'd like to add the adelay filter option allow the audio sync to be changed.

Here's an example command

ffmpeg -i input.mp4 -af "adelay=delays=150:all=1" ouput.mp4

I think using the all option is simplest, otherwise a delay needs to be set for every audio channel (two for stereo, like adelay=150|150).