2760

Focus on just tokenize.
2761

A few more tests converted to the tracing format.
Starting to feel some unease; the tracing tests are harder to read.
Also, already we need extra tracing for debugging.
2762
2763 - simple way to hook into an ostream

It won't handle things like endl (I didn't know endl was a function!)
But don't get side-tracked by that.
2764
2765
2766
2767 - separate traces by layers

I thought we might want the trace to sometimes be stderr or a file,
but now that seems less likely. Backing away from that scenario.
2768 - layers can be used for tests or just debugging
2769
2770
2771
2772
2773 - trace a single layer or all layers at once
2774
2775
2776 - now all tokenize tests are tracified
2777
2778
2779