title: json_extract_scalar fails with parenthesis in key name
body: <p>I've got a string field which contains raw JSON data sent from the server. However, the key contains parenthesis, which seem to be causing issues when trying to extract the data within.</p>
  
  <p>Data Sample:</p>
  
  <pre><code>{"Interview (Onsite)": "2015-04-06 16:58:28"}
  </code></pre>
  
  <p>Extraction Attempt:</p>
  
  <pre><code>timestamp(max(json_extract_scalar(a.status_history, '$.Interview (Onsite)')))
  </code></pre>
  
  <p>(The 'max' function is used as <code>status_history</code> is a repeated field)</p>
  
  <p>Error:</p>
  
  <pre><code>JSONPath parse error at: (Onsite)
  </code></pre>
  
  <p>I've tried multiple common ways of escaping the parenthesis, but it got me nowhere.</p>
  
  <p>Would appreciate suggestions on how to circumvent - I would rather not resort to regex unless I truly have to.</p>