Add a fullInit() function to Suurballe (#181, #323)
to provide faster handling of multiple targets.
A start() function is also added, just for the sake of
convenience.

Rework and improve Suurballe (#323)

- Improve the implementation: use a specific, faster variant of
residual Dijkstra for the first search.
- Some reorganizatiopn to make the code simpler.
- Small doc improvements.

Remove unnecessary integer requirement in Suurballe (#323)