Set in Medellín, “A Poet” is the very funny and occasionally tragic tale of a man for whom art is everything and yet not nearly enough. The writer and director Simón Mesa Soto skewers with knowing precision a kind of devotion to the creative life — without much of the creating — that renders one useless in the real world. The allure of the image of the tortured artist can be so enticing that it obscures the actual art.