Return multiple events from one command

[zenyui]

Is your feature request related to a problem? Please describe.
We have encountered a few scenarios where it would be ideal to return multiple events from a single command.

Describe the solution you'd like
Allow a command handler response to return an ordered array of events, considering backwards compatible / breaking proto changes.

Describe alternatives you've considered
n/a

Additional context
n/a

[zenyui]

I think we should make this backwards compatible in 0.8.X then break it in 0.9.

https://developers.google.com/protocol-buffers/docs/proto3#reserved