Support "reloaded" workflow better

[rafd]

Currently, register-events! clears any existing events and replaces with the given ones.

In the case that all events are in a single namespace, this works fine, because every time that namespace is reloaded, all the changes to the events are captured.

But, when event definitions are across several namespaces, you have to (1) reload the changed event namespace, and (2) remember to also reload the namespace with register-events! (annoying).

Potential solutions:

• don't nuke existing events when calling register-events! (issue: stale events can stick around)
• other alternative?