exthelper: move command declaration into the exthelper
This is necessary to allow sub module to declare commands too.
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