title: Get all derived types of a type
body: <p>Is there a better (more performant or nicer code ;) way to find all derived Types of a Type?
  Currently im using something like:</p>
  
  <ol>
  <li>get all types in used Assemblies</li>
  <li>check my type with all those types if it is 'IsAssignable'</li>
  </ol>
  
  <p>I was wondering if theres a better way todo this?</p>