This module implements the extended greatest common divider algorithm.

Pre: two integers a and b

Post: a tuple (x, y) where a*x + b*y = gcd(a, b) (bezout coefficients)

Pseudo Code: http://en.wikipedia.org/wiki/Extended_Euclidean_algorithm

for a :=131313131, b := 121212121, the benchmark ran in 6.338s:

BenchmarkGetCoeff        1       6255517486 ns/op