doc: integrate graphviz graphs in tutorials
Use the mercurial-docgraph extension (https://pypi.python.org/pypi/hg-
docgraph/) in tutorials in order to have some dot graphs in the tutorials .t
files.
Then generate the doc as usual, the sphinx-graphviz extension (http://www
.sphinx-doc.org/en/stable/ext/graphviz.html) has been added and it should
handle the generation of the graphs. Please be aware that you need the dot
binary installed in your system. Please refer to the extension documentation
for more configuration.