Adding chapters from cli

Issue #87 on hold
created an issue

As far as I can tell from this issue and the current documentation mp3 chapters are supported by eyeD3. Unfortunately I cannot find a way to use the cli to add chapters to my file. If it is implemented, I did not find any documentation about and, but I guess it's not. I'd really like it to be possible to add chapters from cli, because I don't know Python and just want to shell-out from my tool and use eyeD3 for tagging. Its seems to me that someone already implemented it in their fork, but it was never merged. Maybe you could add this, I'd be awesome :)