Release v4.78.0

Added

• Specification given, when append and then events can state their event source and stream with the child lines stream <Source>.<Stream> and, for a keyed stream, streamId = <value>. A then event can assert that it is unrouted with no stream. A routed given or when append states for, checked against the source's identifier type. The executable model refuses these lines with PLAY0268 until a version admits event routes, so they can be authored, printed and checked now. (part of #457)
• New diagnostics: PLAY0547 for a malformed or misplaced route line, PLAY0548 for a route under when <Command>, PLAY0549 for a stream that doesn't resolve or a stream id that doesn't fit it, PLAY0550 for a missing or mistyped for, and PLAY0551 for a route that contradicts the command under test. (part of #457)