Added a few doctests for traversals

[naklecha]

Added a few doctests

>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7

>>> pre_order(root)
1 2 4 5 3 6 7 

>>> in_order(root)
4 2 5 1 6 3 7 

>>> post_order(root)
4 5 2 6 7 3 1 

>>> level_order(root)
1 2 3 4 5 6 7 

>>> level_order_actual(root)
1 
2 3 
4 5 6 7 

>>> pre_order_iter(root)
1 2 4 5 3 6 7 

>>> in_order_iter(root)
4 2 5 1 6 3 7 

>>> post_order_iter(root)
4 5 2 6 7 3 1 

[naklecha]

Thank you!

[cclauss]

Thank you... Your the one who did the work.

[naklecha]

This was my first contribution :)
Is there a method by which I can become a contributor?

[cclauss]

Just keep contributing... Someone will notice. Or ask on Gitter (see README.md)

[naklecha]

Okay! Thanks 👍