Document JSON measurements and omit unavailable memory metrics

src/timer/unix_timer.rs

@@ -77,12 +77,12 @@ impl CPUTimer {
         Self {}
     }
 
-    pub fn stop(&self, child: Child) -> Result<(Time, Time, Information, ExitStatus)> {
+    pub fn stop(&self, child: Child) -> Result<(Time, Time, Option<Information>, ExitStatus)> {
         let (status, usage) = wait4(child)?;
         Ok((
             usage.time_user,
             usage.time_system,
-            usage.memory_usage,
+            Some(usage.memory_usage),
             status,
         ))
     }

src/timer/windows_timer.rs

@@ -84,7 +84,7 @@ impl CPUTimer {
         Self { job_object }
     }
 
-    pub fn stop(&self, mut child: Child) -> Result<(Time, Time, Information, ExitStatus)> {
+    pub fn stop(&self, mut child: Child) -> Result<(Time, Time, Option<Information>, ExitStatus)> {
         let status = child.wait()?;
 
         let mut job_object_info =
@@ -116,9 +116,9 @@ impl CPUTimer {
             let system_time =
                 Time::new::<nanosecond>((job_object_info.TotalKernelTime as f64) * 100.0);
 
-            Ok((user_time, system_time, Information::zero(), status))
+            Ok((user_time, system_time, None, status))
         } else {
-            Ok((Time::zero(), Time::zero(), Information::zero(), status))
+            Ok((Time::zero(), Time::zero(), None, status))
         }
     }
 }