debian: replace clean with override_dh_auto_clean
The current version does not call the default dh_auto_build, which is
a bug. This is required in particular for cleaning the build
directories.
all: tutorials/tutorial.rst static/logo-evolve.ico
sphinx-build . ../html/
tutorials/tutorial.rst: tutorials/tutorial.t
python test2rst.py tutorials/
static/logo-evolve.ico: static/logo-evolve.svg
convert -resize 36x36 static/logo-evolve.svg static/logo-evolve.ico