handle PUT/POST/DELETE to /data/fs/[path] (Fixes #140)

Replacing the earlier PR (#152)
There's something I'm missing here.

This code is inside` chunks.flatMap`, so is not executed until the resulting Process is run, correct? And the resulting Process is the one that the API will run for its effect. But `Process.emitAll` is eager so I'm not sure how that all matches up.

Do I need to put the effects inside the Task that you get by running the result Process? I'm not sure how that would work; I had the impression just having the type `Process[Task, A]` conveyed that was what was happening.