Add Profiler Admin API (#6463)

Two handlers are added to admin API to enable profiling and disable
profiling of a server in a standalone mode, or all nodes in the
distributed mode.

/minio/admin/profiling/start/{cpu,block,mem}:
  - Start profiling and return starting JSON results, e.g. one
    node is offline.

/minio/admin/profiling/download:
  - Stop the on-going profiling task
  - Stream a zip file which contains all profiling files that can
    be later inspected by go tool pprof

vendor/github.com/pkg/profile/README.md

@@ -3,6 +3,9 @@ profile
 
 Simple profiling support package for Go
 
+[![Build Status](https://travis-ci.org/pkg/profile.svg?branch=master)](https://travis-ci.org/pkg/profile) [![GoDoc](http://godoc.org/github.com/pkg/profile?status.svg)](http://godoc.org/github.com/pkg/profile)
+
+
 installation
 ------------
 
@@ -42,3 +45,10 @@ func main() {
 Several convenience package level values are provided for cpu, memory, and block (contention) profiling.
 
 For more complex options, consult the [documentation](http://godoc.org/github.com/pkg/profile).
+
+contributing
+------------
+
+We welcome pull requests, bug fixes and issue reports.
+
+Before proposing a change, please discuss it first by raising an issue.