Not yet right, but worth a snapshot just because it gives a cool result.
Here, try it out:
$ ./translate_mu_debug apps/raytracing/3.mu
$ ./a.elf > x.ppm
Now view x.ppm as an image.
In general, this was quite tedious to write. And a still-open question
is how to emit the progress bar to stderr. My options are to either duplicate
all my print-* functions (already proliferating) or add global variables
to Mu.