Support integrations / alternative build processes

It's been stated already that this is on the roadmap, but obviously lower priority than critical work on Framework itself. Nevertheless, I thought it would be a good idea to keep an issue open for this, as a central point to be referred back to, and to accumulate ongoing thoughts, requests, etc so we all have a shared, clear vision of where this is headed.

(Framework team -- feel free to edit this first message as you see fit)

Roughly estimated, non-committal target date: October? (can be updated over time)

Tasks:
- [ ] Separate Framework into _builder_, _compiler_ and _client_ parts (see below)