title: PHP strip punctuation keep apostrophe
body: <p>Like <a href="https://stackoverflow.com/q/5689918/1112440">PHP strip punctuation</a>, but I want to keep the apostrophe.
  Example:</p>
  
  <pre><code>I'm a student, but I don't like the school. I'll quit school.
  </code></pre>
  
  <p>The string after strip should be:</p>
  
  <pre><code>I'm a student but I don't like the school I'll quit school
  </code></pre>
  
  <p>How can I do that with regular expression or other ways?</p>