Implement link liveness checks #39
Description
As the compendium grows, the entries that point to live web resources (entries that have a url field in the bibtex, i think) might become stale or broken. It would be good to have a routine that checks the "liveness" of any given URL, and flags URLs that are no longer working.
This might be used as part of the publication process, but ideally it would be independent of publication, and could be run regularly (daily? weekly?) in the background, to alert the compendium maintainer of any broken links even during a timespan when no new articles are being added to the compendium.
Since the Internet isn't always reliable, i would be reluctant to have such a system automatically flag entries that are failing to the general public -- it might be failing just for where the check is being run from, or the remote site might be temporarily down for maintenance. The idea here is that the check would alert the maintainer, and the maintainer could figure out what action would be appropriate.