Don't use rust keyword for fake code

[IanConnolly]

As per IRC, fake rust is a bit too similar to real rust.

fn -> func for all code blocks marked notrust.

/cc @steveklabnik

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

[alexcrichton]

Moving assignee to @steveklabnik

[steveklabnik]

Thanks!

[liigo]

Why not fn => function or fn => int?
func is bad here because it's not clear that it means function!

[barosl]

I second function, though I believe it doesn't matter much. We are already using : &int to denote a return type, so whatever the fn keyword may change to, it still requires some knowledge of the existing languages.

[IanConnolly]

I'm not pushed either way, will leave it up to @steveklabnik.

[steveklabnik]

I think it's fine as is.