feat(core): add support for @HostBinding and @HostListener

Example:

@Directive({selector: 'my-directive'})
class MyDirective {
  @HostBinding("attr.my-attr") myAttr: string;
  @HostListener("click", ["$event.target"])
  onClick(target) {
    this.target = target;
  }
}

Closes #3996

modules/angular2/metadata.ts

@@ -40,7 +40,13 @@ export {
   PropertyMetadata,
   Event,
   EventFactory,
-  EventMetadata
+  EventMetadata,
+  HostBinding,
+  HostBindingFactory,
+  HostBindingMetadata,
+  HostListener,
+  HostListenerFactory,
+  HostListenerMetadata
 } from './src/core/metadata';
 
 export {