Add eccentricty-based Madan indices

I added eccentricty-based Madan indices like:
 - eccentric connectivity index,
 - eccentric distance sum,
 - adjacent eccentric distance sum,
 - connective eccentricity,
 - eccentric adjacency,
 - superadjacency,
 - augmented eccentric connectivity.
Merge remote-tracking branch 'origin'

Merging local changes (added eccentric indices) wiht main branch extended with
Wiener index.
Simplify calculation of Wiener index

Wiener index was calculated manually using double 'for' loops. I replace them
with 'sum' function from numpy package.