For Linux/UNIX/macOS you need 'libmagic' installed which is a component of the
'file' utility: <https://github.com/file/file>. You can find out more information
on 'libmagic' and 'file' at this URL: <http://www.darwinsys.com/file/>.

Here are the incantations you must use to get magic for your environment:

- `apt-get install libmagic-dev` on Ubuntu/Debian-ish systems
- `brew install libmagic` on macOS
- `yum install file-devel` on RHEL/CentOS/Fedora

For Windows you will need Rtools <https://cran.r-project.org/bin/windows/Rtools/>
version 3.3 or higher (it may work with older ones, but it's only been tested on
Rtools version 3.3 & 3.4).