D.Combinators: re-export 'atop' from -core
D.Envelope: re-export 'envelope' and 'setEnvelope'
D.Trace: re-export 'trace' and 'setTrace'
D.Envelope: re-export some envelope-related functions from D.Combinators
D.Trace: re-export 'withTrace' from D.Combinators
new module D.Query for re-exporting Query-related things from -core