title: Add padding (or increase height) between section index titles in UITableView
body: <p>I have implemented a section index for my <code>UITableView</code> via the methods <code>sectionIndexTitlesForTableView:</code> and <code>sectionForSectionIndexTitle:</code>. I only have a few sections, and by default they are vertically centered on screen with very little space between each index title. I have seen in other apps where they increase the amount of space between the indexes, not dramatically but at least a few points to give them some breathing room, and increase accuracy when the user tries to tap on the one they want. I would like to know how I can accomplish that?</p>
  
  <p>This is exactly what I want to obtain - notice the extra space between the indexes on the right:</p>
  
  <p><img src="https://i.stack.imgur.com/hTei9.png" alt="enter image description here"></p>