As long as there's been fiction there's been flash fiction, history's most bite-sized form of storytelling that packs theme, character development, and world-building into as small a word-count as possible. It's an art form that's evolved over time—from the earliest fables to "For Sale, Baby Shoes, Never Worn", to Snapchat stories and that 280-character tweet about the good dog you saw at brunch—but in recent years its thrived in a spot pretty much tailor-made for the form: the attention span-deficient world of online horror. From that community …