Checkpoint.
Refactored RiemannSurfacePath code give fast, accurate
validation of Cauchy's theorem.

The RiemannSurfacePath code has been refactored for better
readability and ease of debugging. The RiemannSurfacePath
class now manages a list of RiemannSurfacePath_Segment
objects. The heavy lifting is done by these segment
classes: checkpointing, analytic continuation, integration,
etc.
RiemannSurfacePath refactor seems stable in most cases.

Still need to investigate situations where jumps steps in
the complex x-plane are large, particularly in the case
when the path is around infinity.