title: How to get all NSRange of a particular character in a NSString?
body: <p>I have two NSStrings: <code>orgText</code> and <code>searchLetter</code>.<br>
  I want to highlight every occurrences of the searchLetter in the <code>orgText</code> with a red color.<br>
  How can I get the <code>NSRange</code> of all occurrences of the <code>searchLetter</code> ?<br>
  for eg :</p>
  
  <pre><code>suppose: orgText = "abcahaiapaoiuiapplma"
           searchLetter = "a".
  </code></pre>
  
  <p>I want to hightlight all "a" occurrences in "abcahaiapaoiuiapplma" with red color.<br>
  Thanks.</p>