flatbuffers split

It really, really should be its own package (I assume that's the ultimate attention, but even if this is so, now we have an issue to track). And, at the risk of beating a dead horse, really I am very serious when I say the package in that form is just really, really hard to understand if something goes wrong. I just want to warn that, having had experience with this, unless that package is rewritten to make all the steps a lot more transparent, I seriously doubt that anyone other than @quinnj is going to ever wind up doing much work on it. It's not even necessarily that there's anything overly convoluted going on in reading and writing, it's just nigh on impossible to pick it apart into any kind of manageable pieces.

Start by locating the current flatbuffers package and mapping how its reading and writing responsibilities are organized. Done should mean the functionality is split into its own package and its steps are sufficiently transparent to inspect and debug, but the issue does not identify files or tests.

Written by the indexing model from the issue text.