doc corrections and improvements related to submodules
doc corrections and improvements related to submodules

In particular, add `module+' to the Guide.

original commit: 876bc6f02b05c922a853febc927e76e5dae6daa0

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket