title: C# - Replace Every UpperCase Letter with Underscore and the Letter
body: <p>How do replace Every UpperCase Letter with Underscore and the Letter in C#?
  note: unless the character is already proceeded by a underscore.</p>
  
  <p><strong>UPDATE:</strong>
  For example, 
  MikeJones<br>
  would be turned into<br>
  Mike_Jones  </p>
  
  <p>But Mike_Jones<br>
  would not be turned into<br>
  Mike__Jones  </p>
  
  <p>Is Regex the best approach? Where do I start with this one?</p>