Restructure to eliminate redundant code

[johnothwolo]

I've noticed that each tool has its own filesystem access code. Although Apple's HFS codebase does the same (that codebase is probably 2+ decades old), I do think a lot of the code can be reused and combined into the lib folder, like FreeBSD's libufs.

This will make it easier to addd other utilities to the codebase.

[eafer]

I'm sure you are right, the main purpose of these tools is testing so they are very hacky in many ways. It would be tricky to change things at this point though, so we'll see if I ever get to it.