Update book/ffi to use catch_unwind
Update book/ffi to use catch_unwind

r? @GuillaumeGomez

The doc mentioned to spawn a new thread instead of using catch_unwind, which has been the recommended way to catch panics for foreign function interfaces for a few releases now.
GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust