Use latexmk for building the pdf

This changes the build system from the build script to a makefile using latexmk for building the pdf.

In theory you could make the engine user-specific.
I successfully compiled the pdf using lualtex instead of xelatex as engine.

Now latexmk handles dependencies, takes care of invoking the engine the correct number of times, and so on. Unfortunately latexmk generates a lot of garbage files in doing so, but you could specify a outdir for this.
For now I added those files to the gitignore and the makefile's clean target.

Note: include paths now have to be directory-prefixed; alternatively see e.g. \graphicspath)

(I also had to adapt the bib entry in doing so, because I was getting an error of "too many commas in name", so I grabbed the correct bibtex.)