Release v21.7.0

Changed

• A generated slice now carries every projection it declares, instead of the first one and a diagnostic for the rest. An application whose slice builds several read models - the one a screen binds to and the one a command reads to decide - now gets all of them
• A reducer's read model now stands beside the slice's projections instead of competing with them, so a slice mixing projections and reducers no longer loses most of its read side
• SP0015 no longer reports a second projection in a slice; it is left for the constructs within a projection that the language genuinely has no word for
• SP0020 now says what is actually lost - the read model is carried as a projection over the events the reducer observes, and only the fold itself goes unstated