* Add an Extension_constructor submodule to Obj.
Deprecate top-level functions extension_constructor / extension_name /
extension_id.
* Add 'true' and 'false' to the definition of Bool.t
* Add aliases for the built-in 'list' and 'array' types.
* Add an alias for 'exn' to Printexc.
* Changes entry: built-in type aliases
* Add a Unit module.
* Add paths for built-in exceptions.
yallop