title: Underline text in UIlabel
body: <p>How can I underline a text that could be multiple lines of string?
  I find some people suggest UIWebView, but it is obviously too heavy a class for just text rendering.</p>
  
  <p>My thoughts was to figure out the start point and length of each string in each line.
  And draw a line under it accordingly.</p>
  
  <p>I meet problems at how to figure out the length and start point for the string.</p>
  
  <p>I tried to use <code>-[UILabel textRectForBounds:limitedToNumberOfLines:]</code>, this should be the drawing bounding rect for the text right? 
  Then I have to work on the alignment?
  How can I get the start point of each line when it is center-justified and right justified?</p>