I'm currently writing up a design document and I want to include a number of references to external documents/URLs. I can manually add reference brackets and links so that:
See the external file blah.txt  .... (at bottom of file) References ==========  http://example.com/blah.txt
However this is going to be prone to errors over the document as I add new references. Is there a built-in or 3rd party package to make adding and managing these references easier?