Add numeric algorithm - ModularExponentiation

[aayushborkar14]

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

Merging #263 (b01aa82) into master (9579f56) will increase coverage by 0.63%.
The diff coverage is 97.27%.

@@            Coverage Diff             @@
##           master     #263      +/-   ##
==========================================
+ Coverage   93.64%   94.27%   +0.63%     
==========================================
  Files         123      143      +20     
  Lines        5285     6061     +776     
==========================================
+ Hits         4949     5714     +765     
- Misses        336      347      +11     

Impacted Files	Coverage Δ
Algorithms/Numeric/MillerRabinPrimalityChecker.cs	81.81% <81.81%> (ø)
DataStructures/Timeline.cs	90.19% <86.86%> (-1.65%)	⬇️
DataStructures/Heap/PairingHeap/PairingHeap.cs	98.08% <98.08%> (ø)
DataStructures/AVLTree/AVLTree.cs	98.61% <98.61%> (ø)
Algorithms/Graph/FloydWarshall.cs	100.00% <100.00%> (ø)
Algorithms/Numeric/KeithNumberChecker.cs	100.00% <100.00%> (ø)
Algorithms/Numeric/ModularExponentiation.cs	100.00% <100.00%> (ø)
Algorithms/Sequences/CatalanSequence.cs	100.00% <100.00%> (ø)
Algorithms/Sequences/EulerTotientSequence.cs	100.00% <100.00%> (ø)
Algorithms/Sequences/GolombsSequence.cs	100.00% <100.00%> (ø)
... and 13 more

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[aayushborkar14]

My commit did not cause Travis CI check to fail I believe

[siriak]

Yes, it's a blinking test, I'll deal with that