Investigate classifying caffeine use

[ErikBjare]

Not novel, but should be pretty easy to set up given the overlap with already existing code.

[mrksbrg]

Drinking coffee as we speak. Will try to collect some caffeinated data now.

[oreHGA]

Hey @ErikBjare & @mrksbrg curious - did you ever get to analyzing your caffeine data?

[ErikBjare]

@oreHGA We did not, unfortunately.

I'm still thinking of collecting & analyzing such data though, but haven't had enough reasons to do the work :)