Compiling this package uses Cargo (the package manager of the Rust programming
language) if it is available.  Otherwise, the necessary static library is
downloaded for select operating systems (namely Linux, macOS, and Windows).  In
either case, this is a compile-time dependency only.  Users of the binary
package do **not** need to have Cargo or Rust installed.  Instructions for
installing Cargo are below.

On macOS, Linux, 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:

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

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.

