Merge and Duplicates? Implementation - Person Class 

All tests validated and passing: ✓

Implemented the following business logic:

[app/models/person.rb]
- Implemented Person.merge, taking into account when email does not exist and when email is blank. 

- Also, implemented Person.duplicates?, validating whether the potential duplicate exists before analyzing whether it is a true duplicate or not.

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- Added .DS_Store to .gitignore

- Removed .DS_Store