message: readme: move to Rust 2018
  This updates the README examples to drop the use of `extern crate`. We
  do include instructions to add it, but only for Rust 2015.
  Closes
diff: @@ -32,7 +32,7 @@ Add this to your `Cargo.toml`:
  regex = "1"
  ```
  -and this to your crate root:
  +and this to your crate root (if you're using Rust 2015):
  ```rust
  extern crate regex;
  @@ -42,8 +42,6 @@ Here's a simple example that matches a date in YYYY-MM-DD format and prints the
  year, month and day:
  ```rust
  -extern crate regex;
  -
  use regex::Regex;
  fn main() {
  @@ -66,8 +64,6 @@ If you have lots of dates in text that you'd like to iterate over, then it's
  easy to adapt the above example with an iterator:
  ```rust
  -extern crate regex;
  -
  use regex::Regex;
  const TO_SEARCH: &'static str = "
  @@ -112,9 +108,6 @@ regular expressions are compiled exactly once.
  For example:
  ```rust
  -#[macro_use] extern crate lazy_static;
  -extern crate regex;
  -
  use regex::Regex;
  fn some_helper_function(text: &str) -> bool {
  