UPDATE: Implements CORREL, SLOPE, INTERCEPT, RSQ and STEYX

These are all functions that follow a very simmilar path code

base/src/functions/statistical/mod.rs

@@ -1,6 +1,7 @@
 mod beta;
 mod binom;
 mod chisq;
+mod correl;
 mod count_and_average;
 mod covariance;
 mod devsq;