move ifupdown2/* .

ifupdown2 code was one level deeper because ifupdown2 initially
had ifupdown2 and ifupdown2-addons as two separate packages.
Since they were combined into one package, it makes sense to
move all combined code under the top level directory

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>

docs/source/intro.rst

@@ -0,0 +1,31 @@
+python-ifupdown2
+----------------
+
+The python-ifupdown2 package provides the infrastructure for
+parsing /etc/network/interfaces file, loading, scheduling, template parsing,
+state management and interface dependency generation of interfaces.
+It dynamically loads python addon modules from /usr/share/ifupdownmodules.
+To remain compatible with other packages that depend on ifupdown, it also
+executes scripts under /etc/network/. To make the transition smoother, a
+python module under /usr/share/ifupdownmodules will override a script by
+the same name under /etc/network/. ifupdown2 publishes an interface object which
+is passed to all loadble python addon modules. All lodable modules are
+called for every interface declared in the /etc/network/interfaces file.
+
+Addon modules are responsible for applying interface configuration.
+python-ifupdown2 ships with a set of default addon modules. Each module can
+declare its own set of supported attributes. Each module is passed the iface
+object (which is a representation of /etc/network/interfaces
+iface entry). Each module is also passed the operation to be performed.
+
+Example modules are /usr/share/ifupdownmodules/address.py,
+/usr/share/ifupdownmodules/bridge.py etc
+
+The order in which these modules are invoked is listed in
+/var/lib/ifupdownaddons/addons.conf. There is an ifaddon utility in the works
+to better manage the module ordering.
+
+For more details on adding an addon module, see the section on adding python
+modules. For details on how to write a module, see the api reference and
+development documentation.
+