Turn directories into OCaml modules

An Ocamlbuild plugin that turns directories tagged with "namespace" into a module hierarchy. File names become scoped, so you can have the same filename in multiple directories. So, if you have

server
|-- foo.ml
+-- bar.ml
client
|-- foo.ml
|-- bar.ml
|-- ui
|   +-- reactive.ml
+-- client.ml

It is as if you had written

module Server =
struct
    module Foo = (* server/foo.ml *)
    module Bar = (* server/bar.ml *)
end

module Client =
struct
    module Foo = (* client/foo.ml *)
    module Bar = (* client/bar.ml *)
    module Ui =
    struct
        module Reactive = (* client/ui/reactive.ml *)
    end

    include (* client/client.ml *)
end