vertices don't know which paths computed them

[ofloveandhate]

Bertini_real has an option to save the paths, but no way to know which paths ended at which points. the vertices need to have additional metadata saved: the pathnumbers that computed the vertex.

[ofloveandhate]

This will affect core decomposition, as well as both of the plotting suites, since it means saving more data per vertex. i started a new branch for this improvement. The motivation is making plots for the book project.