R stuff

Invoke like

    ./analyze_benchmarks.R [output/something.tsv]

or

    Rscript ./analyze_benchmarks.R [output/something.tsv]

(No argument uses `output/current.tsv`)
This generates

    output
    ├── something-extremes.tex
    ├── something-norm-col.pdf
    ├── something-norm-shade.pdf
    ├── something.tsv
    └── something.xlsx