cli file loader for Insulet

This works for me. Probably doesn't need much review since it's just a dev tool, but I'm going to mark one place (by commenting the diff in the PR) where I had a question for @kentquirk.

@jh-bate you're welcome to take a look as well.

Note that I didn't change much in `insuletDriver.js` yet - in particular there are a lot of `console.log`s (some commented out, some not), some of which will need to be turned into `debug` calls instead, but in the beginning stages of the work I'll be doing with the Insulet data, the `console.log`s will be more convenient for me since I'll be using the CLI file loader. I *will* change them at a later date, just not as part of this PR.
@kentquirk This buffer conversion is what I had the question on. Took me a while to figure out that it was needed - the canary of failure was the Insulet data processing erroring out on an "unsupported" `ibf_version` because it wasn't actually parsing the right bytes.

I looked back at how you were reading the file in the last (demo) version of Insulet with the UI, and I guess the difference here is between the `FileReader.readAsArrayBuffer` you were using before and Node's file buffers. My question is just whether this (i.e., the `toArrayBuffer` function) is the easiest/best solution. You'll see I appealed to StackOverflow for help...