Investigate option for alternative debug api

[Avaq]

This is just an idea I wanted to write down and come back to later.

Instead of impure debugMode (true) calls before using the rest of Fluture's API, maybe I could provide an alternative to forkCatch, which runs the Future in debug mode.

I dismissed this idea a while ago, because debug context collection already happens before Future interpretation. But I think the performance- and memory- intensive bits only happen during interpretation. If that's the case, this may actually be a viable option.

The benefit of getting rid of debugMode is that Fluture's modukes will be completely pure, and finally truly eligible for tree shaking. See also #343.