title: How to return an array of errors with graphQL
body: <p>How can I return multiple error messages like this ?</p>
  
  <pre><code>"errors": [
    {
      "message": "first error",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "somePath"
      ]
    },
    {
      "message": "second error",
      "locations": [
        {
          "line": 8,
          "column": 9
        }
      ],
      "path": [
        "somePath"
      ]
    },
  ]
  </code></pre>
  
  <p>On my server, if I do <code>throw('an error')</code>, it returns.</p>
  
  <pre><code>"errors": [
    {
      "message": "an error",
      "locations": [
        {
        }
      ],
      "path": ["somePath"]
    }
  ]
  </code></pre>
  
  <p>I would like to return an array of all the errors in the query.
  How can I add multiple errors to the <code>errors</code> array ?</p>