Render self as an SVG image

Property definitions

dot $ DotGraph :: to_svg
	# Render `self` as an SVG image
	fun to_svg: Text do
		var proc = new ProcessDuplex("dot", "-Tsvg")
		var svg = proc.write_and_read(to_dot)
		proc.close
		proc.wait
		return svg
	end
lib/dot/dot.nit:155,2--162,4