New example for evalutions

[Neeratyoy]

What does this PR implement/fix? Explain your changes.

Adds a new example to fetch evaluations.

How should this PR be tested?

The examples/ folder has a new file named fetch_evaluations_tutorial.py.

Any other comments?

Currently, the example shows the following:

• Fetch a task's evaluations
• Create a CDF of predictive accuracy for all runs obtained
• Create box plots to compare the predictive accuracy of the top 10 flows

Would like to have feedback on more additions to the example or plot enhancements.

Thanks.

[codecov-io]

Codecov Report

Merging #688 into develop will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## develop #688 +/- ##
========================================
Coverage 90.35% 90.35% ========================================
Files 36 36 Lines 3785 3785 ========================================
Hits 3420 3420 Misses 365 365

Impacted Files	Coverage Δ
openml/datasets/functions.py	95.66% <ø> (ø)	⬆️

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