Issue #16: Implement Kadane's Algorithm to find the maximum subarray sum

[srinivasboga]

Summary:

Implementing Kadane's Algorithm to find the maximum subarray sum in a given array. With a time complexity of O(n).

Checklist:

• [x] Include a function that takes an array of integers as input and returns the maximum sum of a contiguous subarray.
• [x] Provide test cases to verify the implementation.

Example Test Cases:

• [-2,1,-3,4,-1,2,1,-5,4]
• The output should be 6, as the maximum subarray is [4,-1,2,1].

Additional Notes:

• Added README file with an explanation of the algorithm.