Option for spiral and arc based paths, and other algorithms

[anthony0br]

In real life, roads and railways are made using spirals (for transitions) and arcs (for long continuous curves). The plugin uses bezier curves which can be quite unpredictable in behaviour. I propose an "Algorithm" option where a user can select an algorithm for generating paths.

[anthony0br]

If all suggested algorithms work with just an endpoint, or set of nodes, Curve could become an interface. Then pass the an instance of the type of curve required (Dependency Injection).