[Date Formatters] Make small "r" be a relative date without the prefix/suffix.

As you may or may not know, you can prettify your timestamps (primarily used by bots) by using , for example <t:1:f> will display 1 second after midnught 1 Jan 1970. And that feature is great! I love it.

However, I couldn't help but notice that the R(elative) format (something like xx days ago or in xx days) always forces the prefix/suffix on the date ("in", "ago"). It would be nice to give the developers the flexibility of temoving that prefix/suffix by using the small letter "r", like you do other formats - with "D" for full date and "d" for shortened date. So, accordingly, "r" could output "5 days" so that developers can have the freedom of choosing to implement the prefix themselves or not using it at all (and I know there are such cases when that's needed).

I think that this patch is harmless and, really a minor but important one.