* lisp/image-dired.el (exif): Require.
(image-dired-cmd-read-exif-data-program)
(image-dired-cmd-read-exif-data-options)
(image-dired-get-exif-data): Make obsolete in favour of using
exif.el. This removes a dependency on external exiftool for some
operations.
(image-dired-get-exif-file-name)
(image-dired-thumbnail-set-image-description): Use exif.el
functions instead of exiftool.
* lisp/image/exif.el (exif-tag-alist): Add description and
copyright fields.
* test/lisp/image-dired-tests.el: New file.
* test/lisp/image/exif-tests.el (exif-elem): Move function from here...
* lisp/image/exif.el (exif-field): ...to here, and rename.
(exif-orientation):
* test/lisp/image/exif-tests.el (test-exif-parse)
(test-exif-parse-short): Use above new function.
* lisp/image/exif.el (exif--direct-ascii-value): New function
(bug#40127).
(exif--parse-directory): Use it to get the correct values for
in-directory (i.e., shorter than 4 octets) strings.
* lisp/image/exif.el (exif-parse-buffer): New function.
(exif-orientation): Ditto.
(exif-error): New error symbol, and adjust all error signalling to
only use that signal.
