message: Add semver rule for lints
diff: @@ -31,11 +31,15 @@ fn doit() -> Result<(), Box<dyn Error>> {
  loop {
  // Find a rust block.
  - let (block_start, run_program) = loop {
  + let (block_start, run_program, deny_warnings) = loop {
  match lines.next() {
  Some((lineno, line)) => {
  if line.trim().starts_with("```rust") && !line.contains("skip") {
  - break (lineno + 1, line.contains("run-fail"));
  + break (
  + lineno + 1,
  + line.contains("run-fail"),
  + !line.contains("dont-deny"),
  + );
  }
  }
  None => return Ok(()),
  @@ -73,7 +77,10 @@ fn doit() -> Result<(), Box<dyn Error>> {
  }
  let join = |part: &[&str]| {
  let mut result = String::new();
  - result.push_str("#![allow(unused)]\n#![deny(warnings)]\n");
  + result.push_str("#![allow(unused)]\n");
  + if deny_warnings {
  + result.push_str("#![deny(warnings)]\n");
  + }
  result.push_str(&part.join("\n"));
  if !result.ends_with('\n') {
  result.push('\n');
  