binrep instances for SWChain where Cls a => Cls (SWChain n a).

SW and SWChain can help define binreppable data types plus an "easy to work with" representation in one fell swoop. SWChain is a meaningless newtype only there to help strongweak do its work (without having to write instances manually). So here, we define a bunch of recursive instances that use the inner type.