[WIP] Basic implementation of the harness.

[grynspan]

This PR provides a basic implementation of the harness that spawns child processes and consumes events they produce.

[One line description of your change]

Motivation:

[Explain here the context, and why you're making that change. What is the problem you're trying to solve.]

Modifications:

[Describe the modifications you've done.]

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.