Expand the thread deprecation documentation
Expand the thread deprecation documentation

The story is slightly different for applications vs libraries;
make it clear that libraries should continue using the lock so
we don't break applications that haven't been ported to the
'single thread' model yet.

jessevdk/gtk,Lyude/gtk-,msteinert/gtk,jessevdk/gtk,jessevdk/gtk,Adamovskiy/gtk,davidt/gtk,alexlarsson/gtk,Lyude/gtk-,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,alexlarsson/gtk,chergert/gtk,ebassi/gtk,jigpu/gtk,davidgumberg/gtk,jigpu/gtk,Distrotech/gtk2,jessevdk/gtk,bratsche/gtk-,ahodesuka/gtk,davidgumberg/gtk,davidgumberg/gtk,ahodesuka/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,jigpu/gtk,msteinert/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,Distrotech/gtk2,Lyude/gtk-,grubersjoe/adwaita,bratsche/gtk-,ebassi/gtk,msteinert/gtk,Adamovskiy/gtk,alexlarsson/gtk,bratsche/gtk-,jigpu/gtk,chergert/gtk,davidt/gtk,bratsche/gtk-,Adamovskiy/gtk,jadahl/gtk,Distrotech/gtk2,jessevdk/gtk,bratsche/gtk-,davidt/gtk,grubersjoe/adwaita,alexlarsson/gtk,ahodesuka/gtk,ebassi/gtk,davidt/gtk,davidt/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,Adamovskiy/gtk,chergert/gtk,Adamovskiy/gtk,ahodesuka/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,ebassi/gtk,msteinert/gtk,Adamovskiy/gtk,jadahl/gtk,Lyude/gtk-,Adamovskiy/gtk,Lyude/gtk-,alexlarsson/gtk,chergert/gtk,msteinert/gtk,chergert/gtk,jessevdk/gtk,jigpu/gtk,davidgumberg/gtk,jadahl/gtk,alexlarsson/gtk,davidt/gtk,alexlarsson/gtk,bratsche/gtk-,Lyude/gtk-,ahodesuka/gtk,chergert/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,jadahl/gtk,davidgumberg/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,grubersjoe/adwaita,chergert/gtk,msteinert/gtk,Distrotech/gtk2,Adamovskiy/gtk,ebassi/gtk,davidgumberg/gtk,ebassi/gtk,chergert/gtk,jigpu/gtk,ahodesuka/gtk,Distrotech/gtk2,ahodesuka/gtk,jadahl/gtk,alexlarsson/gtk,jessevdk/gtk,Lyude/gtk-,Distrotech/gtk2