Remove everything `proc_macro` from what will go public 💬 by Caio 4 years ago (log)
I thought the "proc macros need to live in a separate crate" problem
was only a minor annoyance until now: publishing a crate that uses
it implies publishing the proc macro crate too.

This patch works around said annoyance by (mostly manually) reverting
the move to the `tique` module. Now `cantine_derive` is self-contained.

Tree cantine/