Network may now be used with custom controllers.
An example of doing this is in nox.py, which instantiates at TreeNet
using a custom Controller, NoxController, that runs nox_core rather
than the reference controller.
low-level primitives.
The "nox.py" example attempts to use nox as a controller rather than
controller(8).
More edits for INSTALL and README, and refinements for sshd and xterm
examples.