This is particularly useful on operating systems that don't ship
Python as part of the base system (eg. FreeBSD) while still working
just as well as it did before on Linux.

While at it, make it explicit that our scripts are only going to
work with Python 2, and remove the usage of unbuffered I/O, which
as far as I can tell has no effect on the output files.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>

Instead of encoding formatting information inside the
corresponding XSLT stylesheet, use a Python script to reformat
the text appropriately based on a few simple markers.

Splitting the task between the XSLT stylesheet and the Python
script allows us to keep both parts very simple.