Add `OriginalStreamRevision` to ResolvedEvent

[yordis]

Added: OriginalStreamRevision to ResolvedEvent

closes #148

Context

When developing a Optimistic Concurrency Check, I made a mistake that having a function like this one would prevent to some extent:

func getExpectedRevision(opts *Options, lastResolvedEvent *esdb.ResolvedEvent) ExpectedRevision {
    if opts != nil && opts.ExpectedRevision != nil {
        return opts.ExpectedRevision
    } else if lastResolvedEvent == nil {
        return NoStream{}
    } else {
                // I did this
                return Revision(lastResolvedEvent.Event.EventNumber)
    }
}

I changed the samples to reflect the intent.

[yordis]

Done

[yordis]

@YoEight, do you think it is possible to make a release with the latest features?

[YoEight]

Sure, give me a few minutes

[YoEight]

@yordis Done, release v3.3.0 is available with your latest changes!