macros.rs ::core conflicts

[Jaydar]

Using ::core in the tracing 0.1.40 macros.rs file conflicts with other crates.

[mladedav]

Sorry, I don't understand what you mean. Do you have an example?

[kaffarell]

I think this has been fixed on master by #2762. Basically when a user has a crate named core (which btw causes errors with all sort of tooling) the macro.rs paths/imports used (::core::*) will import the wrong core :)