Fix and imporove EnginioReply documentation

Change-Id: I1a111b17b41d5605d2642d022c4d1af9674ba406
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Update changelog

Change-Id: Idfd9db257ab8962c44d3adaa5394c9739b73be58
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>