* lisp/ol-info.el (org-info--link-file-node): New helper to parse info
link info file (manual) name and node.
(org-info-follow-link, org-info-export): Use `org-info--link-file-node'.
(org-info-description-as-command): New function to create description
for info links that may executed to view the manual.
(org-link-parameters): Specify `org-info-description-as-command' as
`:insert-description' for info links.
(org-info-other-documents): Add URL of directory index.
* testing/lisp/test-org-info.el (test-org-info/export): Add cases for
texinfo export with link description.
(test-org-info/link-file-node, test-org-info/description-as-command):
New tests for new functions `org-info--link-file-node' and
`org-info-description-as-command'.
Use recently added :insert-description feature of `org-link'.
Alternative separators between file name and node ":", "::", "#:"
are preserved. Added interpretation of empty path or omitted
file name as info dir index.
* lisp/org-info.el (org-info-export): Handle links when exporting to
"texinfo" back-end.
* lisp/ox-texinfo.el (org-texinfo-link): Delegate "info" links
handling to the function above.