Add more scores/changepoint test statistics

[Tveten]

Additional scores:

• "meanvar" score for detecting changes in mean and/or variance.
• Old "var" score removed. Not well enough understood.
• Custom scores.

[codecov[bot]]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (d250e38) 91.48% compared to head (e105ad4) 94.14%.

Files	Patch %	Lines
skchange/scores/tests/test_scores.py	91.30%	2 Missing :warning:
skchange/change_detectors/moscore.py	93.33%	1 Missing :warning:
skchange/change_detectors/utils.py	66.66%	1 Missing :warning:
skchange/scores/score_factory.py	90.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3 +/- ## ========================================== + Coverage 91.48% 94.14% +2.65% ========================================== Files 13 16 +3 Lines 329 427 +98 ========================================== + Hits 301 402 +101 + Misses 28 25 -3 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.