Added fast-exponentiation algorithm

[svr8]

Functions added:

• fastExponent(base, exponent)
• modularExponent(base, exponent, m)

Files added:

• Algorithm Readme

Files updated:

• Root Readme

[codecov]

Codecov Report

Merging #199 into master will not change coverage.
The diff coverage is 100%.

@@ Coverage Diff @@ ## master #199 +/- ## ===================================== Coverage 100% 100% ===================================== Files 135 137 +2 Lines 2498 2516 +18 Branches 414 416 +2 ===================================== + Hits 2498 2516 +18

Impacted Files	Coverage Δ
...rithms/math/fast-exponentiation/modularExponent.js	100% <100%> (ø)
...lgorithms/math/fast-exponentiation/fastExponent.js	100% <100%> (ø)

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