Setup for building unit tests
Added OUnit hack (borrowed from Frenetic) to get tests running
Added single-node topology parser test
Dot printing includes vertices

- Network to_dot prints vertices as well as edges
- Vertex and Edge signatures include to_dot separate from to_string
- Node and Edge provide correct-ish to_dot implementations
Fixed dot printing of network edges
Added single-edge test
Changed ports to be int64
Added more parser unit tests

- Single bidirectional hop
- Two hops in a row
- Two bidirectional hops in a row