Added gcd function

Author: IPRIT

src/lib/math/greatest-common-divisor/greatest-common-divisor.ts

@@ -1,8 +1,12 @@
 /**
- * Returns greatest common divider from number using iterative Euclid's algorithm
+ * Returns greatest common divider of two numbers
+ * using iterative Euclid's algorithm
+ *
  * @link https://en.wikipedia.org/wiki/Euclidean_algorithm
  *
- * Iterative algorithm much faster (in average ~1.335) than recursive
+ * Iterative algorithm much faster
+ * in average ~1.335 (own benchmarks)
+ * than recursive
  *
  * @param {number} a
  * @param {number} b