Add @export

src/gaussian_smoothing.cpp

@@ -15,6 +15,7 @@ using namespace vigra;
 //' @param x Numeric matrix
 //' @param sigma Scale of the Gaussian kernel
 //' @return Numeric matrix; smoothed version of x
+//' @export
 // [[Rcpp::export]]
 NumericMatrix gaussian_smoothing(NumericMatrix x, double sigma) {
   const int nrows = x.nrow();