Extract subscribe_to_stream function

[jfornoff]

The only persistent subscription functionality is currently subscribing
to all streams. We can allow subscribing to arbitrary streams by
extracting a function that takes the stream name as an argument.

So this is just an extract function refactoring :-)

[drozzy]

I suggest you use $streams here instead. Not sure what the "" will actually accomplish...

[drozzy]

In my PR I removed this completely and replaced it with $streams:
#17

Not sure what it affects, but I verified that aggregate loading/saving works correctly.

[jfornoff]

This PR is intended to be a refactoring, so I did not change any behavior.
@drozzy I'm pretty sure if you do not listen to $all that it probably breaks strong consistency (from what I gather) -- at least if you don't specify which handlers you are specifically waiting for and just set strong_consistency: :true.

[drozzy]

Not sure what you mean by strong consistency. If we assume that one aggregate is one stream - there is no need for inter-aggregate consistency, since aggregate is the only consistency boundary in DDD...
Unless I'm misunderstanding something.

[jfornoff]

I mean this. Its not about aggregates, but event handlers.

[drozzy]

Not sure how you can ensure that all event handlers processed an event... What if the event handler is not using commanded, but rather subscribes directly to EventStore, via Extreme or even .NET?

[jfornoff]

It doesn't work if it is not using Commanded, pretty sure.