Improve module completion annotations

Improve module completion annotations

* sweep.pl (sweep_known_module/1, sweep_is_module/2)
(sweep_module_description_/3, sweep_matching_module/3)
(sweep_module_annotation/2): New predicates.
(sweep_modules_collection/2): Adapt.

* sweeprolog.el (sweeprolog-module-completion-table)
(sweeprolog-module-p, sweeprolog-module-minibuffer-annotation)
(sweeprolog-module-annotation): New functions.
(sweeprolog-modules-collection)
(sweeprolog-read-module-name): Adapt.
(sweeprolog-find-module): Improve feedback for modules that are not
backed by files.