Update minimal Emacs version to 27.1

I tend to keep compatibility with two previous Emacs versions. Given that Emacs
29 has been out for some time, this means Emacs 27 and 28. Emacs 27 came with
Org 9.3, which renames some of the org-link related functions and variables.
These have now been updated in org-ebib.el.

ebib.el

@@ -9,7 +9,7 @@
 ;; Version: 2.40
 ;; Keywords: text bibtex
 ;; URL: http://joostkremers.github.io/ebib/
-;; Package-Requires: ((parsebib "4.0") (emacs "26.1") (compat "29.1.4.3"))
+;; Package-Requires: ((parsebib "4.0") (emacs "27.1") (compat "29.1.4.3"))
 
 ;; Redistribution and use in source and binary forms, with or without
 ;; modification, are permitted provided that the following conditions

org-ebib.el

@@ -96,7 +96,7 @@ entry buffer."
                                         ('key+filename (format "%s@%s" key (ebib-db-get-filename ebib--cur-db :shortened)))
                                         ('key+filepath (format "%s@%s" key (ebib-db-get-filename ebib--cur-db))))))
            (description (ignore-errors (funcall ebib-citation-description-function key ebib--cur-db))))
-      (org-store-link-props :type "ebib"
+      (org-link-store-props :type "ebib"
                             :link link
                             :description description))))
 
@@ -137,14 +137,14 @@ position in the relevant buffer."
       (goto-char position)
       (goto-char (org-element-property :begin (org-element-context)))
       (cond
-       ((looking-at org-bracket-link-regexp)
+       ((looking-at org-link-bracket-re)
         (mapconcat 'org-ebib-make-help-echo-string
                    (split-string
                     (cadr (split-string (match-string-no-properties 1)
                                         ":" t "[[:punct:]]*"))
                     "," t)
                    "\n"))
-       ((looking-at org-plain-link-re)
+       ((looking-at org-link-plain-re)
         (mapconcat 'org-ebib-make-help-echo-string
                    (split-string
                     (cadr (split-string (match-string-no-properties 0)