Improve BST Implementation by adding essential methods & fixing parent ref. issues

[Alokzh]

Changes:

• Fixes class name Type i.e CTBSTNillNode to CTBSTNilNode
• Corrects parent pointer management in all add/remove operations
• Fixes bug in range-finding logic method
• Add new essential methods & tests

[coveralls]

Pull Request Test Coverage Report for Build 16554399675

Details

• 88 of 112 (78.57%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 90.554%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Containers-BinarySearchTree/CTBSTNilNode.class.st	17	29	58.62%
src/Containers-BinarySearchTree/CTBinarySearchTree.class.st	28	40	70.0%

Totals
Change from base Build 16064347857:	0.7%
Covered Lines:	441
Relevant Lines:	487

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💛 - Coveralls