add i/o to readme

src/util/libts.lua

@@ -166,7 +166,9 @@ local function file_exists(fn, errn)
 		return nil
 	end
 end
+local require_memo = {}
 function require(mod)
+	if require_memo[mod] then return unpack(require_memo[mod]) end
 	local fp = mod:gsub('%.', '/')
 	local fns = {
 		'./'..fp..'.lua',      -- local file
@@ -182,7 +184,9 @@ function require(mod)
 	for _,fn in ipairs(fns) do
 		local fne = file_exists(fn, 2)
 		if fne then
-			return dofile(fne, 2)
+			local res = {dofile(fne, 2)}
+			require_memo[mod] = res
+			return unpack(res)
 		end
 	end
 	return _bllua_requiresecure(mod)