Setup a URL shortener

[richierocks]

It would be nice to have short URLs available for linking to RDocumentation.

I want to be able to type something like https://rdocs.io/pkgname/functionname and have it redirect to https://www.rdocumentation.org/packages/pkgname/versions/pkgversion/topics/functionname.

[richierocks]

This would

1. Encourage sharing links, increasing the popularity of the service.
2. Make the links inside our courses easier to read, which would help the Content team and especially me.