Write NetControl framework documentation.

In the process, some of the script documentation of the NetControl
framework was also updated.

doc/frameworks/netcontrol-1-drop-with-debug.bro

@@ -0,0 +1,10 @@
+event NetControl::init()
+	{
+	local debug_plugin = NetControl::create_debug(T);
+	NetControl::activate(debug_plugin, 0);
+	}
+
+event connection_established(c: connection)
+	{
+	NetControl::drop_connection(c$id, 20 secs);
+	}