chore(docs): adding docs to core.ts and annotations.ts

modules/angular2/src/services/app_root_url.ts

@@ -2,10 +2,22 @@ import {Injectable} from 'angular2/di';
 import {isBlank} from 'angular2/src/facade/lang';
 import {DOM} from 'angular2/src/dom/dom_adapter';
 
+/**
+ * Specifies app root url for the application.
+ *
+ * Used by the {@link Compiler} when resolving HTML and CSS template URLs.
+ *
+ * This interface can be overridden by the application developer to create custom behavior.
+ *
+ * See {@link Compiler}
+ */
 @Injectable()
 export class AppRootUrl {
   private _value: string;
 
+  /**
+   * Returns the base URL of the currently running application.
+   */
   get value() {
     if (isBlank(this._value)) {
       var a = DOM.createElement('a');

modules/angular2/src/services/url_resolver.ts

@@ -8,6 +8,13 @@ import {
 } from 'angular2/src/facade/lang';
 import {ListWrapper} from 'angular2/src/facade/collection';
 
+/**
+ * Used by the {@link Compiler} when resolving HTML and CSS template URLs.
+ *
+ * This interface can be overridden by the application developer to create custom behavior.
+ *
+ * See {@link Compiler}
+ */
 @Injectable()
 export class UrlResolver {
   /**