Add support for documentation for macro invocations

[MuhtasimTanmoy]

Problem

• Running cargo clippy with rust.missing_docs = "warn" lint enabled gives an error for the following macros.

  criterion_group!(benches, criterion_benchmark);
  criterion_main!(benches);

How to generate this issue?

• Clippy warning on documentation for macro invocations

Possible solutions:

• Generating documentation in macros
• Rust document macro invocations

Happy to open a PR if needed.

[AliSajid]

I am giving this a thumbs up. I usually develop with rust.missing_docs = "forbid" but I had to go to warn for this so it would build. I'm also happy to contribute.