Tests for Jensen-Shannon and normalization

[AlexDo1]

We need tests for the new metric jensen_shannon. We also need tests for the normalization of entropy, mutual_information and conditional_entropy.
Furthermore, tests for the parameter use_probs, by which entropy, cross_entropy, kullback_leibler and jensen_shannon allow probabilities as input, would be nice.

Tests

• Jensen-Shannon (divergence and distance)
• Normalization of entropy, mutual information and conditional entropy
• use_probs parameter