Result streams & out-of-band return values

[kovasb]

Need a generic way to handle values other than the result of the evaluation.

The first use case is stdout and stderr. Want those streamed into the UI as they are happening.

Other use cases are progress indicators, or other streams that result from the computation that you want to see as the computation is happening.

Aspects of the problem include

1. Should these be stored in datomic? If so, how? Should they be in their own database or partition?
2. What are the hooks in the user code? Lamina channels?
3. What is an extensible way to deal with this in the UI?