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

spec/source-map.js

@@ -1,8 +1,7 @@
-/*global CompilerContext, Handlebars */
 try {
   if (typeof define !== 'function' || !define.amd) {
     var SourceMap = require('source-map'),
-          SourceMapConsumer = SourceMap.SourceMapConsumer;
+         SourceMapConsumer = SourceMap.SourceMapConsumer;
   }
 } catch (err) {
   /* NOP for in browser */
@@ -20,13 +19,13 @@ describe('source-map', function() {
     equal(!!template.map, !CompilerContext.browser);
   });
   it('should map source properly', function() {
-    var source = '  b{{hello}}  \n  {{bar}}a {{#block arg hash=(subex 1 subval)}}{{/block}}',
-        template = Handlebars.precompile(source, {destName: 'dest.js', srcName: 'src.hbs'});
+    var templateSource = '  b{{hello}}  \n  {{bar}}a {{#block arg hash=(subex 1 subval)}}{{/block}}',
+        template = Handlebars.precompile(templateSource, {destName: 'dest.js', srcName: 'src.hbs'});
 
     if (template.map) {
       var consumer = new SourceMapConsumer(template.map),
           lines = template.code.split('\n'),
-          srcLines = source.split('\n'),
+          srcLines = templateSource.split('\n'),
 
           generated = grepLine('"  b"', lines),
           source = grepLine('  b', srcLines);
@@ -43,7 +42,7 @@ function grepLine(token, lines) {
     var column = lines[i].indexOf(token);
     if (column >= 0) {
       return {
-        line: i+1,
+        line: i + 1,
         column: column
       };
     }