Add DEBUG_HIDE_TTY_DATE env var (#486)

Squashed commit of the following:

commit 62589c0
Author: Adrian Mejia <admejiar@cisco.com>
Date:   Sat Aug 12 15:24:45 2017 -0400

    solves merge conflict

commit 55e5c5e
Author: Adrian Mejia <admejiar@cisco.com>
Date:   Sat Aug 12 15:21:16 2017 -0400

    docs

commit e09dec3
Author: Adrian Mejia <admejiar@cisco.com>
Date:   Sat Aug 12 15:19:10 2017 -0400

    cleanup

commit 9dd6a2b
Author: Adrian Mejia <admejiar@cisco.com>
Date:   Sat Aug 12 15:05:53 2017 -0400

    enables DEBUG_HIDE_TTY_DATE

Author: TooTallNate

Diff for: README.md

@@ -1,5 +1,5 @@
 # debug
-[![Build Status](https://travis-ci.org/visionmedia/debug.svg?branch=master)](https://travis-ci.org/visionmedia/debug)  [![Coverage Status](https://coveralls.io/repos/github/visionmedia/debug/badge.svg?branch=master)](https://coveralls.io/github/visionmedia/debug?branch=master)  [![Slack](https://visionmedia-community-slackin.now.sh/badge.svg)](https://visionmedia-community-slackin.now.sh/) [![OpenCollective](https://opencollective.com/debug/backers/badge.svg)](#backers) 
+[![Build Status](https://travis-ci.org/visionmedia/debug.svg?branch=master)](https://travis-ci.org/visionmedia/debug)  [![Coverage Status](https://coveralls.io/repos/github/visionmedia/debug/badge.svg?branch=master)](https://coveralls.io/github/visionmedia/debug?branch=master)  [![Slack](https://visionmedia-community-slackin.now.sh/badge.svg)](https://visionmedia-community-slackin.now.sh/) [![OpenCollective](https://opencollective.com/debug/backers/badge.svg)](#backers)
 [![OpenCollective](https://opencollective.com/debug/sponsors/badge.svg)](#sponsors)
 
 <img width="647" src="https://user-images.githubusercontent.com/71256/29091486-fa38524c-7c37-11e7-895f-e7ec8e1039b6.png">
@@ -149,6 +149,7 @@ change the behavior of the debug logging:
 | `DEBUG_COLORS`| Whether or not to use colors in the debug output. |
 | `DEBUG_DEPTH` | Object inspection depth. |
 | `DEBUG_SHOW_HIDDEN` | Shows hidden properties on inspected objects. |
+| `DEBUG_HIDE_TTY_DATE` | Hide date from debug output on TTY. |
 
 
 __Note:__ The environment variables beginning with `DEBUG_` end up being
@@ -269,7 +270,7 @@ enabled or disabled.
  - TJ Holowaychuk
  - Nathan Rajlich
  - Andrew Rhyne
- 
+
 ## Backers
 
 Support us with a monthly donation and help us continue our activities. [[Become a backer](https://opencollective.com/debug#backer)]

Diff for: src/node.js

@@ -115,8 +115,15 @@ function formatArgs(args) {
     args[0] = prefix + args[0].split('\n').join('\n' + prefix);
     args.push(colorCode + 'm+' + exports.humanize(this.diff) + '\u001b[0m');
   } else {
-    args[0] = new Date().toISOString()
-      + ' ' + name + ' ' + args[0];
+    args[0] = getDate() + name + ' ' + args[0];
+  }
+}
+
+function getDate() {
+  if (exports.inspectOpts.hideTtyDate) {
+    return '';
+  } else {
+    return new Date().toISOString() + ' ';
   }
 }