Cleanup of doc files.

Fixed xterm.py (and cleanup) to clean up screen sessions.
Cleaned up sshd.py (though interface is still in flux.)
Added 1024-node network example (treenet1024.py).
Added example showing multiple tests on a single network (multitest.py).
Renamed examples to make them easier to type!

examples/cli.py

@@ -0,0 +1,10 @@
+#!/usr/bin/python
+
+"Create a tree network and run the CLI on it."
+
+from mininet import init, TreeNet, Cli
+
+if __name__ == '__main__':
+   init()
+   network = TreeNet( depth=2, fanout=4, kernel=True )
+   network.run( Cli )