org-capture.el: Use %\n instead of %n.

org-capture.el: Use %\n instead of %n.

* org-capture.el (org-capture-fill-template): Use %\n instead of %n as a
template element to be replaced with the nth prompted string.
(org-capture-templates): Update docstring.

* org.texi (Template expansion): Update doc to reflect change.

Using %n triggers errors when the template contains escaped strings,
which happens a lot with links.