title: Check if line ends with punctuation; if not, add period
body: <p>I want to check if a line ends with a punctuation (.,?!) and if it doesn't, then add a period.</p>
  
  <pre><code>A button is missing!
  A button on their back allowed them to hug
  A cat is carried by the scruff of its neck by a teenage boy?
  A cattery is where cats are commercially housed
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>A button is missing!
  A button on their back allowed them to hug.
  A cat is carried by the scruff of its neck by a teenage boy?
  A cattery is where cats are commercially housed.
  </code></pre>
  
  <p>I'm really stumped, I tried grepping the last character of a string -- any help?</p>