bearriver: Offer all definitions from FRP.Yampa.Random #423
Description
The module FRP.Yampa.Random is being offered by Yampa, but not bearriver.
This makes the interface offered by bearriver not compliant with Yampa, therefore not delivering on the promise of being API-compatible.
This is a subissue of #40. Because #40 is a big issue, it's good to split it in several smaller ones.