Object associated to a polynomial system.

- BasePoint: the parameter point defining some system
- Edges: a mutable list of edges
- Graph: a HomotopyGraph containing the node
- PartialSols: PointArray of solutions for SpecializedSystem
- SpecializedSystem: list of equations for system specialized at the BasePoint

The object HomotopyNode is a type, with ancestor classes MutableHashTable < HashTable < Thing.