title: can't get service instance from $injector.get()
body: <p>I define a customer service named "greeting", but can't get the instance from $injector.get('greeting'). It will throw such error: <em>Unknown provider: greetingProvider &lt;- greeting</em>. So which is the right way to get it? Following is the code:</p>
  
  <pre><code>var app = angular.module('myDI', []);
  app.config(function($provide){
      $provide.provider('greeting', function(){
          this.$get = function(){
               return function(name) {
                   console.log("Hello, " + name);
              };
          };
      });
  });
  
  var injector = angular.injector();
  var greeting = injector.get('greeting');
  greeting('Ford Prefect');
  </code></pre>