org-attach: Attach files specified in a dired buffer.
* lisp/org-attach.el (org-attach-attach-files): New.
(org-attach-dired-marked-files-in-dired): New
(org-attach-dired-marked-files-or-file-at-cursor-in-dired): New.
(org-attach-dired-attach-to-next-best-subtree): New command.
(org-attach-dired-attach-to-next-best-subtree-cp): New command.
(org-attach-dired-attach-to-next-best-subtree-mv): New command.
(org-attach-dired-attach-to-next-best-subtree-ln): New command.
(org-attach-dired-attach-to-next-best-subtree-lns): New command.
* testing/lisp/test-org-attach.el: Tests.