full script 3 review

This is only script 3 in-depth review (done previously by Tarun, not me).

Includes:

• layout updates for using TOC
• multiple minor typos, content and code bugs fixes (e.g. correct for no shuffling on cross_val_score by default)
• some code simplifications (e.g. no numpy.random)
• extension for shuffling and stratification on splits, both train/test and CV (includes use of explicit cross-validator)

changed the description

added 14 commits

• 6fefb862...c67cad36 - 13 commits from branch improvements_uwe
• 1563d739 - Merge branch 'improvements_uwe' into mik_review_script_3

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added 1 commit

• 5ecec6d5 - minor corrections post review by Uwe

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merged

mentioned in commit 1ad38a3f