Having a file with the same name as its package creates hard-to-diagnose
import error, so rename mininet.py to net.py.  This commit moves utility
functions, generally those dealing with network namespaces and interface
management, into their own file.

Also fix a few minor formatting bugs and clean up logging code (which
had issues when multiple files would import mininet.logging_mod).

Make much of the Mininet code object-oriented around the new Mininet
object, and create a generic way to build a Mininet.

Previously, each network topology was created by Mininet API calls,
which seems much less approachable for new users than passing in a
topology object along with controller, switch, and host classes.

The modified code is all in ripcordtest.py, but will need to replace the
main mininet.py code eventually.

Kernel-space support only, for now.

Forgot to add __init__.py

Use customized StreamHandler from Python logging module to print
only messages for the specified loglevel to the console.

Don't print retry errors by default.

Was causing OSErrors because the process to kill no longer existed.

Much faster now; from 1 s delay to 100 us.

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

PYTHONPATH mods are no longer required for installation.

Useful for monitoring the output of a set of nodes.

- invoke ofdatapath with --fail=closed (no controller = no connectivity!)
- stop hosts before switches before the controller
	- this seems slightly more sensible
	- it's the reverse of the startup order
- fix retry() so it kind of works (it's actually helpful I think!)

Added retry() function for createLink to see if it helps (probably won't.)
Random edits to docs.

Added commentary on control network to mininet.py.
Hopefully fixed linearbandwidth.py for real.

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.

instantiate a mininet Network based on its topology.

Also minor cleanup of nox.py and GridNet class in mininet.py.

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.