Build the graph

Property definitions

nitc $ InheritanceGraph :: draw
	# Build the graph
	fun draw(parents_depth, children_depth: nullable Int): DotGraph do
		draw_node center
		draw_parents(center, parents_depth)
		draw_children(center, children_depth)
		return graph
	end
src/doc/commands/commands_graph.nit:213,2--219,4