http://blog.janosilles.com/2017/01/my-command-prompt/
https://crates.io/crates/rustup_prompt_helper
https://github.com/ijanos/rustup_prompt_helper
https://github.com/rust-lang-nursery/rustup.rs/issues/720
https://www.reddit.com/r/rust/comments/5qb88d/show_rrust_rustup_prompt_helper/