Added DS/Lowest Common Ancestor

[PrachiSharma12]

Implemented Lowest Common Ancestor

Fixed #46

Type of change

Please check options that are relevant to your PR.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New Data Structure
• [x] New Algorithm

Checklist:

• [x] I have squashed my commits
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My code is a working bug-free code

[ay2306]

There are multiple methods of finding the Lowest Common Ancestor in general for example binary lifting or RMQ approach.