Stephen King has been scaring the spit out of us for half a century now. This year marks the 50th anniversary of the publication of his first novel, “Carrie,” the scalding tale of a teenage girl whose pyrotechnic powers are provoked by high school cruelty. Since then, King, 76, has published more than 70 bestselling books of fiction, sometimes as many as three in one year, dozens of which have become movies or TV series. He’s conjured up our chills with small-town vampires, haunted hotels, possessed cars, revenant pets — much of the success of his fiction grows from his ability to anchor horro…