Don't unlink/rmdir via the VFS; manipulate state internally.  It's not
really useful if we only learn that runtime state is no longer valid
whenever we react to getattr() or readdir(), so don't worry about this
feature.
Forgot to add runfs core state
Add tests for making directories and a tree of directories
Remove dead OS-specific code
Merge branch 'master' of https://github.com/jcnelson/runfs
Remove inotofy/kqueue notification as a design goal