Changes for Reactive Controller

This pull request includes several changes to the public API that are necessary to implement an OpenFlow 1.0 controller that can provide a substitute for NetKAT choice in the form of "reactive" fast-failover. Specifically:

* Expose a features stage for use with the OpenFlow0x01 Controller;
* Expose the `SDN_OpenFlow0x01` module;
* Fix a bug in `PortStatus` parsing (#81);
* Expand QuickCheck round trip testing.

This is related to the branch of the same name in the frenetic repository.