Minimal example for Rust bug #15823

Re-exported type aliases are not preserved in function signatures

Problem

1. utils crate contains type alias type Frequency = u64
2. sub crate uses utils crate and exposes fn cpu_frequency() -> io::Result<Frequency>
3. facade crate aggregates all these crates and reexports both type alias and function
4. rustdoc fails to use Frequency type alias for re-exported cpu_frequency function

This behavior was tested both with Rust 1.41.0-stable and 1.43.0-nightly (7760cd0fb 2020-02-19)