New cost matrix computation implementation

New behaviour to define how cost matrix is computed : 

- default, same as before : `cost_matrix` in lap_cost_matrice.py function  will be called with three parameters:
   - max_disp : maximum velocity
   - cost_function : a function which will process final matrix
   - parameters given to `distance.cdist` scipy function, used to compute distance matrix

- new behaviour : 
   - user define `cost_matrix_function` which have this API func(pos0, pos1, dt, **custom_params)
   - user also need to define max_cost manually