add AMD loader

Author: jhudson8

index.js

@@ -1,11 +1,22 @@
-Chart.React = {
-  Bar: require('./bar'),
-  Doughnut: require('./doughnut'),
-  Line: require('./line'),
-  Pie: require('./pie'),
-  PolarArea: require('./polar-area'),
-  Radar: require('./radar')
-};
-
-  
+(function(main) {
+    if (typeof Chart === 'function') {
+        // script include
+        main(Chart);
+    } else  {
+        // AMD
+        define([], function() {
+            return main;
+        });
+    }
+})(function(Chart) {
+  Chart.React = {
+    Bar: require('./bar'),
+    Doughnut: require('./doughnut'),
+    Line: require('./line'),
+    Pie: require('./pie'),
+    PolarArea: require('./polar-area'),
+    Radar: require('./radar')
+  };
+  return Chart;
+});