Add paper "Performance of Python runtimes on a non-numeric scientific co...

This is the paper associated to the "Py vs. Py" poster.

The `.rst` is converted to LaTeX without errors, but I cannot compile
the generated LaTeX without hand-editing the file.  In particular:

- the rst2latex converter inserts blank lines here and there, where
  TeX does not expect them;

- tables are particularly affected by this, as blank lines (hence,
  `\par`) are inserted amid the items on a single line;

- figures need to be better positioned and resized.

I can produce the figures in any other format supported by Matplotlib.