FAQ on "How do I return a closure from a function?" no longer correct because impl Fn

[FranklinChen]

https://www.rust-lang.org/en-US/faq.html#how-do-i-return-a-closure-from-a-function is no longer correct because now it is possible to return a closure without boxing it thanks to returning impl Fn.

[est31]

It should probably also mention that if the closure doesn't capture anything, you can return a function pointer now, as non capturing closures coerce to function pointers.

[pietroalbini]

The FAQ is managed on the rust-lang/rust-www repo. Can you open an issue there? Thanks!