I added a simple performance-measuring tool, `tools/time-ent`.  It runs
ent a couple of different ways, against a known entomologist-data branch
(specified by a commit in the regular entomologist-data branch in this
repo).  That script gives a rough, over-all measurement of how long
different ent commands take.

More detailed information, including the call tree and flame graph,
can be gathered like this:

```
$ perf record -g -F 999 ent tag 7e2a3a59fb6b77403ff1035255367607
$ perf script -F +pid > /tmp/test.perf
```

Then upload the `test.perf` file to the firefox visualizer at
<https://profiler.firefox.com/>.

A local visualizer would be nice, i'm sure there is one somewhere.