By calling die() instead of propagating error unions. Not surprising
that error propagation has a performance impact, but I was hoping it
wasn't this bad.
Import performance was already quite good, but now it's even better!
With the one test case I have it's faster than JSON import, but I expect
that some dir structures will be much slower.
This isn't the low-memory browsing experience I was hoping to implement,
yet, but it serves as a good way to test the new format and such a
sink-based import is useful to have anyway.
Performance is much better than I had expected, and I haven't even
profiled anything yet.
