In our time of simmering enchantment with all things culinary, from cookbooks to gastro memoirs to televised chef brawls, you may be forgiven for thinking our food obsession is some kind of recent phenomenon. Massimo Montanari, in “Let the Meatballs Rest: And Other Stories About Food and Culture,’’ demonstrates how spectacularly unrecent, how truly untrendy this mania turns out to be. Positively medieval is more like it.