H2JVM - A Haskell Library for writing JVM Bytecode

@evincar wondering your thoughts (and anyone else’s of course!) on making the MonadFix approach the only way to emit labels. I think this would make the UnmarkedLabel error mostly impossible (apart from weird cases like sharing labels across CodeBuilders, which could be prevented with a state variable like ST does). However it also forces a certain style upon users, which might be a bit off putting and make the library less approachable. What are your thoughts?