Step3: Linked src files and Reading negatives edges

[codeSG]

Tasks

1. Create src & include files for dealing negative edges with pgr_bellmanFord

   • Create src/bellman_ford_neg.c
   • Create src/bellman_ford_neg_driver.cpp
   • Create include/drivers/bellman_ford_neg_driver.h

2. Function to read negative_edge_sql

   • Function to add a negative cost edge : graph_add_neg_edge()
   • Function called by pgr_bellman_hpp (Here) : insert_negative_edges()