Add support for switch topology discovery

This pull request adds a new stage for OpenFlow 1.0-based controllers that will accumulate topology information for switches in what is being called a "NIB". This method uses ethernet packets whose payload describes the origin switch and destination of a packet. Once that packet reaches another switch, it will be sent to the controller, at which point the controller has all the information it needs to infer the connection between switches.

Currently, the information stored in the "NIB" cannot be queried. That is a task left for after #91 is resolved.

This pull request depends on #90.

Closes #88.