latexmk v4.40

From [its homepage](http://users.phys.psu.edu/~collins/software/latexmk-jcc/), `latexmk` “is a perl script for running LaTeX the correct number of times to resolve cross references, etc”. This is *not* the same as [`latex-mk`](http://latex-mk.sourceforge.net/). It’s well [maintained][versions] (first release in 2001, latest one in January, 2014) and [widly][u1] [used][se]. It’s packaged in [Debian][].

[versions]: http://users.phys.psu.edu/~collins/software/latexmk-jcc/versions.html
[u1]: http://www.tjansson.dk/2008/10/writing-large-latex-documents-in-vim/
[se]: https://tex.stackexchange.com/tags/latexmk/hot
[Debian]: https://packages.debian.org/sid/latexmk
Use: ```
(testpath/"test.tex").write <<-EOS.undent
...
EOS
```