printf also autothreads.
printf also autothreads.

And after almost 18 months and hundreds of commits, this closes #2632 and the whole 6.d spec is documented.
It's been a daunting task, but the Rakulang community has pulled it off. Congrats!

tbrowder/doc,tbrowder/doc,MasterDuke17/doc,tbrowder/doc,MasterDuke17/doc,tbrowder/doc,MasterDuke17/doc,MasterDuke17/doc