Add leftwise flatMap operator for Decoded
Add leftwise flatMap operator for Decoded

This version of the operator was left out for some reason. This wasn't
intentional, so we're just correcting the oversight.

alskipp/Argo,ojolabs/Argo,thoughtbot/Argo,ojolabs/Argo,alskipp/Argo,thoughtbot/Argo,thoughtbot/Argo,alskipp/Argo,ojolabs/Argo