added new implementation of semaphore used for process synchronization.
added new folder named "operating_system" with two subfolders 1) scheduling and 2) process_synchronization
created new file semaphore.py in subfolder process_synchronization

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
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• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
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