Add version expectancy support to Append command

[hecrj]

What about something like this?

tasks.try { tasks.append.by_id(task_id).expecting_version(3).call(events) }

I guess that the expecting_version method should be exposed by the Append command, as it only makes sense there, right? Should we rename the command to Create to make it consistent with other adapters?

[solnic]

I'd vote for renaming it to Create to make it consistent. Re expecting_version I've no idea what it does :)

[hecrj]

I'll rename it then :D

Re expecting_version When you are adding new events to a stream you can specify the version in which you expect the stream to be. Normally, this version is the event number of the last event you've read from the stream. Thus, if between reading and writing someone has added some more events, your write will fail (actually, it could pass if the events that collide had the same uuids).