Create scikit-learn decision tree examples to visualize

[OlivierBinette]

Create scikit-learn decision tree examples alongside with "wants" for their visualization.

[OlivierBinette]

We can pick datasets, classification and regression tasks, fit decision trees, and describe what we'd like in a visualization of these trees.

[fleurfanli]

Visualized the classification of the sklearn iris data set in this notebook. Content:

• Tree plots with different settings
• Text representation
• Visualize decision boundaries

[OlivierBinette]

@fleurfanli Thanks this looks great! Let's used these fitted trees as visualization examples and for tests.