Remove 'extern crate proc_macro' from example code

Author: dtolnay

.github/workflows/ci.yml

@@ -12,11 +12,13 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.31.0]
+        rust: [nightly, beta, stable, 1.42.0, 1.31.0]
     steps:
       - uses: actions/checkout@v2
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{matrix.rust}}
+      - if: matrix.rust == '1.31.0'
+        run: echo 'extern crate proc_macro;' >> demo-hack-impl/src/lib.rs
       - run: cargo run --manifest-path example/Cargo.toml
       - run: cargo test --all

README.md

@@ -33,8 +33,6 @@ The function signature is the same as for ordinary function-like procedural
 macros.
 
 ```rust
-extern crate proc_macro;
-
 use proc_macro::TokenStream;
 use proc_macro_hack::proc_macro_hack;
 use quote::quote;

demo-hack-impl/src/lib.rs

@@ -1,5 +1,3 @@
-extern crate proc_macro;
-
 use proc_macro::TokenStream;
 use proc_macro_hack::proc_macro_hack;
 use quote::quote;

src/lib.rs

@@ -31,8 +31,8 @@
 //! macros.
 //!
 //! ```
-//! extern crate proc_macro;
-//!
+//! # extern crate proc_macro;
+//! #
 //! use proc_macro::TokenStream;
 //! use proc_macro_hack::proc_macro_hack;
 //! use quote::quote;