FIXED: Correctly recognize DCG grammar rules in 'C-c C-d'

FIXED: Correctly recognize DCG grammar rules in 'C-c C-d'

* sweeprolog.el (sweeprolog-beginning-of-predicate-at-point): Also
return the module and neck operator of the predicate at point.
(sweeprolog-insert-predicate-documentation)
(sweeprolog-read-predicate-documentation-function)
(sweeprolog-read-predicate-documentation-with-holes)
(sweeprolog-read-predicate-documentation-default-function)
(sweeprolog-read-predicate-documentation)
(sweeprolog-document-predicate-at-point): Adapt to support DCGs and
non-local predicates.