“Anvil! The Anvil Story” takes so many untelegraphed turns that it’s impossible to predict. The most unexpected thing is how inexplicably sweet the guys are, how truly touching their hopes and dreams, and how much we pull for them to make it on their terms. The filmmaker masterfully builds the narrative, adding salient biographical details and snippets of interviews captured on the fly, dropped like tantalizing breadcrumbs on our journey. I’m far from a metalhead; I’d never even heard of Anvil before seeing this documentary. Like another terrific metal band documentary, “Metallica: Some Kind of Monster,” this film doesn’t pander to fans. It goes deep and leaves us thinking about our own lives, our own relationships, and even – gulp – the meaning of life. Who’d a thunk it?