add profiler support

profiling is now available via the HTTP base URL /debug/pprof/

examples, use this URL to start and download a 30 seconds CPU profile:

/debug/pprof/profile?seconds=30

use this URL to profile used memory:

/debug/pprof/heap?gc=1

use this URL to profile allocated memory:

/debug/pprof/allocs?gc=1

Full docs here:

https://golang.org/pkg/net/http/pprof/

cmd/portable.go

@@ -91,6 +91,7 @@ Please take a look at the usage below to customize the serving parameters`,
 				LogMaxAge:     defaultLogMaxAge,
 				LogCompress:   defaultLogCompress,
 				LogVerbose:    defaultLogVerbose,
+				Profiler:      defaultProfiler,
 				Shutdown:      make(chan bool),
 				PortableMode:  1,
 				PortableUser: dataprovider.User{