[Binary Tree] Different views of binary tree added (#6965)

* Different views of binary tree added

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* mypy errors resolved

* doc test for remaining functions

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* Example moved in if block

* doctest cases added

* Cases from if block removed

* Update data_structures/binary_tree/diff_views_of_binary_tree.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update data_structures/binary_tree/diff_views_of_binary_tree.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* PR Comments resolved

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* flake8 warning resolved

* Changes revered

* flake8 issue resolved

* Put the diagrams just above the doctests

* Update diff_views_of_binary_tree.py

* Update diff_views_of_binary_tree.py

* I love mypy

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Co-authored-by: Christian Clauss <cclauss@me.com>