Finalize listing captions

involved raggedleft and using \discretionary to allow breaking at ::

listing.lua

 function rust_listing (dir, subpath)
-	local module_name = subpath:gsub(".tex$",""):gsub("mod$",""):gsub("/","::")
-	--module_name = module_name:gsub((".?"):rep(47) .. "::", "%1\\breakline{}" )
-	local caption = "\\texttt{" ..  module_name .. "}"
+	local module_name = subpath
+		:gsub(".tex$","")
+		:gsub("mod$","")
+		:gsub("/","\\discretionary{}{::}{::}")
+
+	local caption = "\\raggedleft \\texttt{" ..  module_name .. "}"
+
 	return (
 		"\\lstinputlisting["
-			.. "caption={" .. caption .. "}"
-		.. "]{" .. dir .. subpath .. "}"
+		.. "caption={" .. caption .. "}"
+	.. "]{" .. dir .. subpath .. "}"
 	)
 end