MAINT prepare new release

[mfeurer]

This PR updates the changelog and bounces the version number. Ideally, we merge #853 before doing a new release.

[PGijsbers]

I'll finish #851 today so we can merge that too.

[codecov-io]

Codecov Report

Merging #855 into develop will decrease coverage by 0.09%.
The diff coverage is 100%.

@@ Coverage Diff @@## develop #855 +/- ##
=========================================
- Coverage 88.49% 88.4% -0.1% 
=========================================
Files 37 37 Lines 4269 4269 =========================================
- Hits 3778 3774 -4 - Misses 491 495 +4

Impacted Files	Coverage Δ
openml/__version__.py	100% <100%> (ø)	⬆️
openml/datasets/functions.py	94.06% <0%> (-1.25%)	⬇️
openml/flows/functions.py	86.85% <0%> (-0.58%)	⬇️
openml/runs/functions.py	82.59% <0%> (+0.27%)	⬆️

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