Chris Willman Music WriterCan a band that seems to operate under rigid and even blatantly joyless conditions still produce music that sparks spontaneous ecstasy in listeners? That’s the sort of question that might not seem unusual if it were a classical ensemble we were talking about, or the ballet. But in a new documentary about the group King Crimson, it’s legendary guitar player Robert Fripp, as tough a taskmaster as anyone in the so-called finer arts, Robert Fripp, who’s keeping the musicians in his hire perpetually on pointe.“In the Court of the Crimson King” is really about as good as rock documentaries get, in capturing the essence of a group of musicians and how they relate to each other, the world and a muse whose demands result in literal and figurative calluses.