No more anonymous trait fn parameters

[mark-i-m]

cc rust-lang/rust#41686

These were the only ones I could find from a quick search, but please let me know if there are others.

cc @Centril

[Centril]

We should probably also document the change itself in the reference, i.e. that in Rust 2015 it is like this, and in Rust 2018 it is like that.

LGTM otherwise -- I defer to you on coverage =)

[Havvy]

These changes are good, but doesn't document the RFC. Thanks!

[mark-i-m]

@Havvy are you telling me "LGTM, except you should document the RFC" or "LGTM, please don't document the RFC"?

[Centril]

Before we close the tracking issue we need to document the changes themselves :)

[Havvy]

Typo (from phone). Also meant to merge but failed to do so when I wrote it. If the RFC actually makes it an error, it should be documented. We dont have any policy in place yet for depreciations, though one could be suggested with a PR.

[Centril]

The RFC did not specify the migration strategy; but the language team resolved it in favor of making it a hard error in Rust 2018 and that is what the compiler does when you enable edition 2018.