dud: A dub replacement

[Sebastiaan Koppe]

On Monday, 18 November 2019 at 09:53:56 UTC, Paolo Invernizzi 
wrote:
> A win-win move would be to have dud emit the other formats 
> automatically as part of the compilation procedure, so to have 
> always all of them present and synced on the content.

I already regret starting about this. Instead of rooting for the 
SDL format, I should have just recommended to deprecate the json 
one.