Documentation cannot link to external URLs that end in .md

Per joerg84: "In fact it seems that all links ending with .md are interpreted as
relative links on the webpage, i.e. [label](https://test.com/foo.md) is
rendered into <a href="/documentation/latest/https://test.com/foo/
">label</a>"

Currently the rakefile will rewrite all with this too general regex

'''f.read.gsub(/\((.*)(\.md)\)/, '(/documentation/latest/\1/)')'''