Add full support for es6

Converts the tool chain to use babel, eslint, and webpack vs. the previous proprietary solutions.

Additionally begins enforcing additional linting concerns as well as updates the code to reflect these rules.

Fixes #855
Fixes #993

lib/handlebars/utils.js

@@ -1,11 +1,11 @@
 /*jshint -W004 */
 var escape = {
-  "&": "&",
-  "<": "&lt;",
-  ">": "&gt;",
-  '"': "&quot;",
-  "'": "&#x27;",
-  "`": "&#x60;"
+  '&': '&amp;',
+  '<': '&lt;',
+  '>': '&gt;',
+  '"': '&quot;',
+  "'": '&#x27;',
+  '`': '&#x60;'
 };
 
 var badChars = /[&<>"'`]/g;
@@ -31,6 +31,7 @@ export var toString = Object.prototype.toString;
 
 // Sourced from lodash
 // https://github.com/bestiejs/lodash/blob/master/LICENSE.txt
+/*eslint-disable func-style */
 var isFunction = function(value) {
   return typeof value === 'function';
 };
@@ -42,6 +43,7 @@ if (isFunction(/x/)) {
   };
 }
 export var isFunction;
+/*eslint-enable func-style */
 
 /* istanbul ignore next */
 export var isArray = Array.isArray || function(value) {