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/runtime.js

@@ -1,6 +1,6 @@
-module Utils from "./utils";
-import Exception from "./exception";
-import { COMPILER_REVISION, REVISION_CHANGES, createFrame } from "./base";
+import * as Utils from './utils';
+import Exception from './exception';
+import { COMPILER_REVISION, REVISION_CHANGES, createFrame } from './base';
 
 export function checkRevision(compilerInfo) {
   var compilerRevision = compilerInfo && compilerInfo[0] || 1,
@@ -10,12 +10,12 @@ export function checkRevision(compilerInfo) {
     if (compilerRevision < currentRevision) {
       var runtimeVersions = REVISION_CHANGES[currentRevision],
           compilerVersions = REVISION_CHANGES[compilerRevision];
-      throw new Exception("Template was precompiled with an older version of Handlebars than the current runtime. "+
-            "Please update your precompiler to a newer version ("+runtimeVersions+") or downgrade your runtime to an older version ("+compilerVersions+").");
+      throw new Exception('Template was precompiled with an older version of Handlebars than the current runtime. ' +
+            'Please update your precompiler to a newer version (' + runtimeVersions + ') or downgrade your runtime to an older version (' + compilerVersions + ').');
     } else {
       // Use the embedded version info since the runtime doesn't know about this revision yet
-      throw new Exception("Template was precompiled with a newer version of Handlebars than the current runtime. "+
-            "Please update your runtime to a newer version ("+compilerInfo[1]+").");
+      throw new Exception('Template was precompiled with a newer version of Handlebars than the current runtime. ' +
+            'Please update your runtime to a newer version (' + compilerInfo[1] + ').');
     }
   }
 }
@@ -25,7 +25,7 @@ export function checkRevision(compilerInfo) {
 export function template(templateSpec, env) {
   /* istanbul ignore next */
   if (!env) {
-    throw new Exception("No environment passed to template");
+    throw new Exception('No environment passed to template');
   }
   if (!templateSpec || !templateSpec.main) {
     throw new Exception('Unknown template object: ' + typeof templateSpec);
@@ -35,7 +35,7 @@ export function template(templateSpec, env) {
   // for external users to override these as psuedo-supported APIs.
   env.VM.checkRevision(templateSpec.compiler);
 
-  var invokePartialWrapper = function(partial, context, options) {
+  function invokePartialWrapper(partial, context, options) {
     if (options.hash) {
       context = Utils.extend({}, context, options.hash);
     }
@@ -61,9 +61,9 @@ export function template(templateSpec, env) {
       }
       return result;
     } else {
-      throw new Exception("The partial " + options.name + " could not be compiled when running in runtime-only mode");
+      throw new Exception('The partial ' + options.name + ' could not be compiled when running in runtime-only mode');
     }
-  };
+  }
 
   // Just add water
   var container = {
@@ -97,34 +97,34 @@ export function template(templateSpec, env) {
       var programWrapper = this.programs[i],
           fn = this.fn(i);
       if (data || depths || blockParams || declaredBlockParams) {
-        programWrapper = program(this, i, fn, data, declaredBlockParams, blockParams, depths);
+        programWrapper = wrapProgram(this, i, fn, data, declaredBlockParams, blockParams, depths);
       } else if (!programWrapper) {
-        programWrapper = this.programs[i] = program(this, i, fn);
+        programWrapper = this.programs[i] = wrapProgram(this, i, fn);
       }
       return programWrapper;
     },
 
-    data: function(data, depth) {
-      while (data && depth--) {
-        data = data._parent;
+    data: function(value, depth) {
+      while (value && depth--) {
+        value = value._parent;
       }
-      return data;
+      return value;
     },
     merge: function(param, common) {
-      var ret = param || common;
+      var obj = param || common;
 
       if (param && common && (param !== common)) {
-        ret = Utils.extend({}, common, param);
+        obj = Utils.extend({}, common, param);
       }
 
-      return ret;
+      return obj;
     },
 
     noop: env.VM.noop,
     compilerInfo: templateSpec.compiler
   };
 
-  var ret = function(context, options) {
+  function ret(context, options) {
     options = options || {};
     var data = options.data;
 
@@ -139,7 +139,7 @@ export function template(templateSpec, env) {
     }
 
     return templateSpec.main.call(container, context, container.helpers, container.partials, data, blockParams, depths);
-  };
+  }
   ret.isTop = true;
 
   ret._setup = function(options) {
@@ -163,13 +163,13 @@ export function template(templateSpec, env) {
       throw new Exception('must pass parent depths');
     }
 
-    return program(container, i, templateSpec[i], data, 0, blockParams, depths);
+    return wrapProgram(container, i, templateSpec[i], data, 0, blockParams, depths);
   };
   return ret;
 }
 
-export function program(container, i, fn, data, declaredBlockParams, blockParams, depths) {
-  var prog = function(context, options) {
+export function wrapProgram(container, i, fn, data, declaredBlockParams, blockParams, depths) {
+  function prog(context, options) {
     options = options || {};
 
     return fn.call(container,
@@ -178,7 +178,7 @@ export function program(container, i, fn, data, declaredBlockParams, blockParams
         options.data || data,
         blockParams && [options.blockParams].concat(blockParams),
         depths && [context].concat(depths));
-  };
+  }
   prog.program = i;
   prog.depth = depths ? depths.length : 0;
   prog.blockParams = declaredBlockParams || 0;
@@ -199,14 +199,14 @@ export function resolvePartial(partial, context, options) {
 export function invokePartial(partial, context, options) {
   options.partial = true;
 
-  if(partial === undefined) {
-    throw new Exception("The partial " + options.name + " could not be found");
-  } else if(partial instanceof Function) {
+  if (partial === undefined) {
+    throw new Exception('The partial ' + options.name + ' could not be found');
+  } else if (partial instanceof Function) {
     return partial(context, options);
   }
 }
 
-export function noop() { return ""; }
+export function noop() { return ''; }
 
 function initData(context, data) {
   if (!data || !('root' in data)) {