Replace customizable boolean with hook instead

This could provide the user with more freedom in parsing reftex label
candidates

company-reftex.el

@@ -71,9 +71,10 @@ See `reftex-format-citation'."
   :type '(choice (const :tag "Off" nil) integer)
   :group 'company-reftex)
 
-(defcustom company-reftex-labels-parse-all t
-  "Whether to rescan labels in entire document."
-  :type 'boolean
+(defcustom company-reftex-parse-labels-hook '(reftex-parse-all)
+  "Hook to be run for parsing reftex labels."
+  :type 'hook
+  :options '(reftex-parse-all reftex-parse-one)
   :group 'company-reftex)
 
 (defcustom company-reftex-labels-regexp
@@ -230,9 +231,7 @@ For more information on COMMAND and ARG see `company-backends'."
 
 (defun company-reftex-label-candidates (prefix)
   "Find all label candidates matching PREFIX."
-  (if company-reftex-labels-parse-all
-      (reftex-parse-all)
-    (reftex-parse-one))
+  (run-hooks 'company-reftex-parse-labels-hook)
   (cl-loop for entry in (symbol-value reftex-docstruct-symbol)
            if (and (stringp (car entry)) (string-prefix-p prefix (car entry)))
            collect