Now, to reference mininet files, use 'import mininet.mininet'.

PYTHONPATH mods are no longer required for installation.

Not sure if I want nox_core -v in nox.py - it's useful for debugging.
ripcordtest.py (and grid.py) still depend on routing, which I haven't been
able to test yet.

Unfortunately, I can't test this at the moment since nox seems not to
be able to find the routing module.

Added/renamed examples: grid.py, tree1024.py

Added -v flag to nox arguments, so we have some chance of figuring
out why nox is dying, as it generally is.

ripcord.py was a name conflict - ugh!
This one creates a network successfully, but ping doesn't work with
nox out of the box at least.