Software prerequisites: apt-cacher-ng debiman mandoc python3

After installing apt-cacher-ng, the proxy is started automatically and should be
listening on port 3142.
debiman by default will download from http://localhost:3142/deb.debian.org/
This setting can be changed with -local_mirror or -remote_mirror

Download manpages from Debian:

    $ DEBIMAN_SERVING_DIR=/absolue/path make download

Extract all the pages from .gz:

    $ DEBIMAN_SERVING_DIR=/absolue/path make download

Convert manpages to plaintext:

    $ DEBIMAN_SERVING_DIR=/absolue/path make convert

Create RDF graph:

    $ DEBIMAN_SERVING_DIR=/absolue/path ./rdf.py