add trigger info analyzer

[goto-bus-stop]

Wrote this while working on a94d6ae05462d5b152e43860e94131bf8dbe804a. Figuring out what goes wrong in a function that only skips bytes is pretty hard. With the extra structure provided by a full reader like this, it's much easier to see where it goes wrong, fix it in the full reader, and then tweak the numbers in the skipping function.

[goto-bus-stop]

Most of this was "ported" from https://github.com/mullikine/aokts/, btw.