The Language of Flowers, by Vanessa Diffenbaugh, made the rounds on the book club circuit not too long ago, evoking strong feelings for many. “I feel it’s only fair to warn you, dear reader, that Vanessa Diffenbaugh’s central character … is going to break your heart three ways from Sunday,” writes Paula McLain (Circling the Sun, The Paris Wife). “She’s also going to make you want …