buffer: add includes() for parity with TypedArray

Add Buffer#includes() by wrapping an indexOf and performing a strict
equals check to -1.

The includes method takes the search value, byteOffset, and encoding as
arguments.

The test is a modified version of the indexOf test.

Fixes: https://github.com/nodejs/node/issues/3552
PR-URL: https://github.com/nodejs/node/pull/3567
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/buffer.js

@@ -488,6 +488,11 @@ Buffer.prototype.indexOf = function indexOf(val, byteOffset, encoding) {
 };
 
 
+Buffer.prototype.includes = function includes(val, byteOffset, encoding) {
+  return this.indexOf(val, byteOffset, encoding) !== -1;
+};
+
+
 Buffer.prototype.fill = function fill(val, start, end) {
   start = start >> 0;
   end = (end === undefined) ? this.length : end >> 0;