New metrics are added for imbalanced data

[mcavs]

Mathews Correlation Coefficient, Balanced Accuracy, Brier Score and log-loss metrics, which are used in case of imbalanced data, are added.

[hbaniecki]

Thanks!

[pbiecek]

@mcavs thank you,
for onboarding of new code please:

• add unit tests that will cover these additional functions to https://github.com/ModelOriented/DALEX/tree/master/tests
• add proper documentation (i.e. to https://modeloriented.github.io/DALEX/reference/model_performance.html)
• update https://github.com/ModelOriented/DALEX/blob/master/NEWS.md

[mcavs]

@pbiecek 2 added and 3 updated, but I do not know how to add unit test :/

[hbaniecki]

Hi @mcavs, I could try to add unit tests, but I don't see changes with respect to 2. & 3. (only the code changed looking at https://github.com/ModelOriented/DALEX/pull/480/files).

[mcavs]

Hi @mcavs, I could try to add unit tests, but I don't see changes with respect to 2. & 3. (only the code changed looking at https://github.com/ModelOriented/DALEX/pull/480/files).

Hi @hbaniecki, I created a new pull request consists 2 and 3. You can see it on #505