Improve performance by making sure `add` is inlined

src/average.rs

@@ -37,6 +37,7 @@ impl Average {
     }
 
     /// Add an element sampled from the population.
+    #[inline]
     pub fn add(&mut self, sample: f64) {
         // This algorithm introduced by Welford in 1962 trades numerical
         // stability for a division inside the loop.

src/weighted_average.rs

@@ -40,6 +40,7 @@ impl WeightedAverage {
     }
 
     /// Add a weighted element sampled from the population.
+    #[inline]
     pub fn add(&mut self, sample: f64, weight: f64) {
         // The algorithm for the unweighted average was suggested by Welford in 1962.
         // The algorithm for the weighted average was suggested by West in 1979.