Compiling this package uses Cargo (the package manager of the Rust programming
language) if it is available.  Version 1.31.0 or newer is required.  Otherwise,
the necessary static library is downloaded for select operating systems (namely
Linux, macOS, and Windows running on x86_64).  In either case, this is a
compile-time dependency only.  Users of the binary package do **not** need to
have Cargo or Rust installed.  Below is installation help on some platforms.

On Linux, macOS, and other Unix-like OSes,

   - Run the following in the terminal:  curl https://sh.rustup.rs -sSf | sh

   OR, using your operating system's package manager, run one of the following:

   - sudo apt install cargo (Debian/Ubuntu)
   - sudo dnf install cargo (Fedora/CentOS)
   - brew install rust (macOS)

On Windows,

   - Download rustup-init.exe from https://win.rustup.rs
   - In the terminal, run:  rustup-init.exe -y --default-host x86_64-pc-windows-gnu
   - Restart the terminal (so the new terminal picks up changes to your PATH).
   - In a new terminal, run:  rustup target add i686-pc-windows-gnu
   - Restart R (so it picks up changes to your PATH) and install this package.

