Use https for links where available
As some of our links are suggestions to install add-on software, insecure links potentially allow an attacker to replace this with their malware.

During the process of writing this, I also found and fixed some broken or semi-broken (e.g. redirected to the top level instead of the page we want) links.

The following (already) broken links remain:
http://nipunbatra.github.io/2015/06/timeseries/ + others from this site
http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/CUJ/1992/9210/ross/ross.htm
http://mysite.verizon.net/aesir_research/date/jdalg2.htm