Move to timer module

src/timer/wall_clock_timer.rs

@@ -0,0 +1,20 @@
+use std::time::Instant;
+
+use crate::util::units::Second;
+
+pub struct WallClockTimer {
+    start: Instant,
+}
+
+impl WallClockTimer {
+    pub fn start() -> WallClockTimer {
+        WallClockTimer {
+            start: Instant::now(),
+        }
+    }
+
+    pub fn stop(&self) -> Second {
+        let duration = self.start.elapsed();
+        duration.as_secs() as f64 + f64::from(duration.subsec_nanos()) * 1e-9
+    }
+}