Updating the Prim Ref page

[Willy Tschager]

I think we shoud have some text explaining why there is a mix of "rin" and "ring" in the ring-primitives.

The correct nomenclature is to use the full word "ring". 
Due to the fact that too many files would be affected, it was decided to keep "rin" primitives in the library.
All files using "ri" has been moved, to use "ring".

Good point. Added!

w.