add generators support via regenerator

test/fixtures/syntax/generators/simple/actual.js

@@ -0,0 +1,19 @@
+function *range(max, step) {
+  var count = 0;
+  step = step || 1;
+
+  for (var i = 0; i < max; i += step) {
+    count++;
+    yield i;
+  }
+
+  return count;
+}
+
+var gen = range(20, 3), info;
+
+while (!(info = gen.next()).done) {
+  info.value;
+}
+
+assert(info.value, 7);