Added Implementation of GCD of two numbers using Euclidean Algorithm

[Subhoshri]

Description

• Created a function GCD to calculate the Greatest Common Divisor of two numbers 'a' and 'b' using Euclidean Algorithm.
• It handles edge cases of (0,1), (1,0) and (0,0) well.

Tasks Completed

• Added the files gcd_euclidean_algorithm.py, gcd_euclidean_algorithm.java and gcd_euclidean_algorithm.cpp in the corresponding directory
• My code aligns with the specified structure.
• Updated RoadMap.md

[imsuraj675]

Make these modifications:

• Your code's logic is inconsistent. In Cpp and java, gcd(-2, -4) will give 2, but in python it will return -2. GCD means the largest number which divides both the numbers, so answer of gcd(-2, -4) should be equal to 2.
• Gcd(0,0) = 0. Don't return, as -1

[Subhoshri]

I have made the required changes.

[imsuraj675]

Good work