What used to be `tools/emul/user.h` was in fact specific to zasm, so I
moved it there.
To avoid name confusion, I renamed what used to be kernel.h and user.h
to kernel-bin.h and user-bin.h.
On build, pack `parts/z80` into a CFS and embed it into the emulated
zasm executable as an fsdev. This will allow for the upcoming include
directive to have something to go to.
For now, this is useless except for inflating the emulated zasm's size.
With the help of the newly-introduced cfspack tool, we can mount a
filesystem in our emulated shell and play around. Read-only for now.
Unpacking incoming.
