Outline should handle URIs

[zmughal]

Outline might not refer to pages in the current document.

example:

$ wget http://www.maa.org/sites/default/files/images/images/upload_library/22/Ford/knuth403-422.pdf
$ mutool show ~/Downloads/knuth403-422.pdf outline 2>&1 | tail -5
                Reviews (null)
                        Review: untitled [pp. 482-486]  http://www.jstor.org/stable/2325110?origin=JSTOR-pdf
                        Review: untitled [pp. 486-489]  http://www.jstor.org/stable/2325111?origin=JSTOR-pdf
                Telegraphic Reviews [pp. 490-495]       http://www.jstor.org/stable/2325112?origin=JSTOR-pdf
                Back Matter     http://www.jstor.org/stable/2325113?origin=JSTOR-pdf