Amazon has released the trailer for Invincible, a new animated (and R-rated) superhero series starring the voice talent of Steven Yeun and J.K. Simmons. The eight-episode hour-long show comes from Robert Kirkman, adapting his own comic book series, who you might also recognize as the creator of a little indie comic turned TV series The Walking Dead. Invincible follows Mark Grayson (Yeun), a totally normal 17-year-old who also happens to be the son of Earth's mightiest superhero, Omni-Man (Simmons). Yes, much like another recently-announced Amazon show, this kind've sounds a …