Additional community evaluation scores

[GiulioRossetti]

Add relevant community evaluation scores.

List of requests collected via email (to check for applicability, some seems not to apply to network clustering):

• Silhouette score,
• Davies-Bouldin (DB) index,
• Calinski-Harabasz index(CH)
• Dunn Index
• Directed-weighted modularity
• ...

Please integrate and fill missing references.