document kronecker (#7)

Author: oscardssmith

README.md

@@ -8,3 +8,4 @@ This library adds several functions useful for doing math on integers. Most of t
 * `ispower(x::Integer)` return if there are integer `base` and `exponent>1` values such that `base^exponent = x`.
 * `find_exponent(x::Integer)` returns the largest possible integer `exponent` such that `base^exponent = x` for some `base`. Returns `1` for `x ∈ [0,1]`.
 * `is_probably_prime(x::Integer; reps=25)` returns if `x` is prime. Will be incorrect less than `4^-reps` of the time.
+* `kronecker(a::Integer, n::Integer)` Computes the [Kronecker_symbol](https://en.wikipedia.org/wiki/Kronecker_symbol) which is a generalization of the legendre and jacobi symbols.