Skip copyright in mscgen figs

Suggest to add the option to skip copyright marker for mscgen figures.

scripts/msc_to_img.lua

@@ -4,7 +4,7 @@
 
 local function mscgenToPng(mscgen, charttype)
 	local fname = "tmp.png"
-	local png = pandoc.pipe("mscgen", {"-T", "png", "-q", "-o", fname, "-S", charttype}, mscgen)
+	local png = pandoc.pipe("mscgen", {"-T", "png", "-q", "-o", fname, "-S", charttype, "--nocopyright"}, mscgen)
 	local f = io.open(fname, "rb")
 	local contents = f:read "*a"
 	f:close()