Mgattozzi/whorl: single file, std only, async Rust executor

just a fyi

//! What whorl isn't: //! - Performant, this is an adaptation of a class I gave at Rustconf a few //! years back. Its first and foremost goal is to teach how an executor //! works, not the best way to make it fast. Reading the tokio source //! code would be a really good thing if you want to learn about how to make //! things performant and scalable.