Move away from original number rounding convention

As the number conversion for the original problem was somewhat weird + arguably somewhat Java-specific (see discussions at gunnarmorling/1brc#5), I've decided to move away from using that and use the sample results + run checks against my own base implementation instead.

samples/measurements-3.out

@@ -1 +1 @@
-{Bosaso=-15.0/1.3/20.0, Petropavlovsk-Kamchatsky=-9.5/0.0/9.5}
+{Bosaso=-15.0/1.2/20.0, Petropavlovsk-Kamchatsky=-9.5/0.0/9.5}

samples/measurements-rounding.out

@@ -1 +1 @@
-{ham=14.6/25.5/33.6, jel=-9.0/18.0/46.5}
+{ham=14.6/25.4/33.6, jel=-9.0/17.9/46.5}

src/main.rs

@@ -18,7 +18,7 @@ struct WeatherStationStats {
 }
 impl WeatherStationStats {
     fn mean(&self) -> f64 {
-        ((self.sum) / (self.count as f64) * 10.0).ceil() / 10.0
+        self.sum / self.count as f64
     }
 }
 fn parse_line(line: &str) -> (&str, f64) {