ADDED: in-buffer completions for predicate options

ADDED: in-buffer completions for predicate options

* sweep.pl (sweep_option_functors_collection/2)
(sweep_options_collection/2)
(sweep_option_arguments_collection/2): New predicates.
(sweep_context_callable_arg/4): Recognize predicate options.

* sweeprolog.el (sweeprolog-option-functor-completion-candidates)
(sweeprolog-option-completion-candidates)
(sweeprolog-option-arg-completion-candidates): New functions, used in...
(sweeprolog--atom-or-functor-completion-at-point): ...here.

* sweep.texi (Code Completion): Document predicate options completion.
* sweeprolog-tests.el: Test it.