Restore CPU usage report format

Commit 78435f8 changed the existing output format for the CPU usage
from `cpu usage:` to `cpu usage (all):`.

This might break existing scripts relying on this format. Revert that
part of the change and only report the CPU usage for the given period
with a suffix:

cpu usage:	0.087%
cpu usage (1s):	1.42%

Author: tklauser

README.md

@@ -79,23 +79,21 @@ The output displays:
 
 Note that processes running the agent are marked with `*` next to the PID (e.g. `4132*`).
 
-#### $ gops \<pid\> [seconds] 
+#### $ gops \<pid\>
 
-To report more information about a process, run `gops` following by a PID:
-> If set the seconds arg, the percent of the CPU time this process uses within given time duration will be reported.
+To report more information about a process, run `gops` followed by a PID:
 
 ```sh
 $ gops <pid>
-parent PID:	  5985
-threads:	  27
-memory usage:	  0.199%
-cpu usage(all): 0.139%
-cpu usage(1s):	  19.5% # if seconds provided
-username:	  jbd
-cmd+args:	  /Applications/Splice.app/Contents/Resources/Splice Helper.app/Contents/MacOS/Splice   Helper -pid 5985
-local/remote:	  127.0.0.1:56765 <-> :0 (LISTEN)
-local/remote:	  127.0.0.1:56765 <-> 127.0.0.1:50955 (ESTABLISHED)
-local/remote:	  100.76.175.164:52353 <-> 54.241.191.232:443 (ESTABLISHED)
+parent PID:	5985
+threads:	27
+memory usage:	0.199%
+cpu usage:	0.139%
+username:	jbd
+cmd+args:	/Applications/Splice.app/Contents/Resources/Splice Helper.app/Contents/MacOS/Splice Helper -pid 5985
+local/remote:	127.0.0.1:56765 <-> :0 (LISTEN)
+local/remote:	127.0.0.1:56765 <-> 127.0.0.1:50955 (ESTABLISHED)
+local/remote:	100.76.175.164:52353 <-> 54.241.191.232:443 (ESTABLISHED)
 ```
 
 #### $ gops tree

main.go

@@ -146,11 +146,11 @@ func processInfo(pid, interval int) {
 		fmt.Printf("memory usage:\t%.3f%%\n", v)
 	}
 	if v, err := p.CPUPercent(); err == nil {
-		fmt.Printf("cpu usage(all):\t%.3f%%\n", v)
+		fmt.Printf("cpu usage:\t%.3f%%\n", v)
 	}
 	if interval > 0 {
 		if v, err := cpuPercentWithinTime(p, time.Second*time.Duration(interval)); err == nil {
-			fmt.Printf("cpu usage(%ds):\t%.3f%%\n", interval, v)
+			fmt.Printf("cpu usage (%ds):\t%.3f%%\n", interval, v)
 		}
 	}
 	if v, err := p.Username(); err == nil {