[Feature] output upcoming track to upcomingTrack text file

[bonelifer]

Feature request for outputting upcoming track so that external 3rd party apps can access that information.

[PromyLOPh]

We’re kind of hitting the limits of the eventcmd “serialization format” here, but the branch eventcmd-upcoming has a working implementation. Is that what you were looking for?

[bonelifer]

This request was facilitated by my patiobar feature request to be able to show the upcoming artist -title on the page.
kylejohnson/Patiobar#43 I don't always want to go to another room just to look at the terminal. So this would be helpful there.

[PromyLOPh]

I merged the branch into master. Enjoy :)