feat(binary): removing browser buffer support

Removes the fallback to UInt8Array if Buffer does not exist
(a.k.a. on web). Now requires user to polyfill Buffer

BREAKING CHANGE:
Removes out-of-box support for Binary serialization on web platforms.
Users will have to polyfill node Buffer type

lib/bson/binary.js

@@ -1,11 +1,5 @@
 'use strict';
 
-if (typeof Buffer !== 'undefined') {
-  var bufferConstructor = new Buffer(1) instanceof Uint8Array ? Buffer : Uint8Array;
-} else {
-  bufferConstructor = Uint8Array;
-}
-
 /**
  * Module dependencies.
  * @ignore
@@ -16,7 +10,7 @@ function convert(integer) {
 }
 
 function toExtendedJSON(obj) {
-  var base64String = typeof Buffer !== 'undefined' ? obj.buffer.toString('base64') : obj.toBase64();
+  var base64String = obj.buffer.toString('base64');
 
   return {
     $binary: {
@@ -29,16 +23,7 @@ function toExtendedJSON(obj) {
 function fromExtendedJSON(BSON, doc) {
   var type = doc.$binary.subType ? parseInt(doc.$binary.subType, 16) : 0;
 
-  if (typeof Buffer !== 'undefined' && bufferConstructor === Buffer) {
-    var data = new Buffer(doc.$binary.base64, 'base64');
-  } else {
-    data = new Uint8Array(
-      BSON.Binary
-        .fromBase64(doc.$binary.base64)
-        .split('')
-        .map(c => c.charCodeAt(0))
-    );
-  }
+  var data = new Buffer(doc.$binary.base64, 'base64');
 
   return new BSON.Binary(data, type);
 }