title: When use poolConnection or CreateConnection felixge/node-mysql
body: <p>I use <a href="https://github.com/felixge/node-mysql" rel="noreferrer">https://github.com/felixge/node-mysql</a> for my application 
  When and Why use</p>
  
  <pre><code>db_pool = mysql.createConnection(db);
  </code></pre>
  
  <p>or </p>
  
  <pre><code>db_pool = mysql.createPool(db);
  </code></pre>
  
  <p>what are the differences? and when to use them?</p>