message: fix(compiler) Make it compile with no_std + core.
diff: )
  )]
  +#[cfg(all(not(feature = "std"), feature = "core"))]
  +extern crate alloc;
  +
  mod lib {
  - #[cfg(not(feature = "std"))]
  + #[cfg(all(not(feature = "std"), feature = "core"))]
  pub mod std {
  - #[cfg(feature = "core")]
  - pub use alloc::{boxed, fmt, string, vec};
  -
  - #[cfg(feature = "core")]
  + #[macro_use]
  + pub use alloc::{boxed, string, vec};
  + pub use core::fmt;
  pub use hashbrown as collections;
  }
  