reference: that looks better without those abbreviations

Author: tshepang

src/doc/reference.md

@@ -2831,13 +2831,13 @@ on the right-hand side.
 An example of an `as` expression:
 
 ```
-# fn sum(v: &[f64]) -> f64 { 0.0 }
-# fn len(v: &[f64]) -> i32 { 0 }
+# fn sum(values: &[f64]) -> f64 { 0.0 }
+# fn len(values: &[f64]) -> i32 { 0 }
 
-fn avg(v: &[f64]) -> f64 {
-  let sum: f64 = sum(v);
-  let sz: f64 = len(v) as f64;
-  return sum / sz;
+fn average(values: &[f64]) -> f64 {
+  let sum: f64 = sum(values);
+  let size: f64 = len(values) as f64;
+  sum / size
 }
 ```