title: Compilation errors with ImageResizer 3.2.1
body: <p>After allowing Nuget to update ImageResizer 3.1.5 to version 3.2.1 my compiles are failing with multiple errors (all same type):</p>
  
  <pre><code>Error 5 Missing compiler required member 'System.Runtime.CompilerServices.ExtensionAttribute..ctor'
  </code></pre>
  
  <p>Apparently this is the result of an assembly version mismatch. Deleting all ImageResizer references in the project allows an error-free compile.</p>
  
  <p>Reverting to ImageResizer 3.1.5 also allows a successful compilation.</p>
  
  <p>My project is a simple MVC3 application targeting .NET4  - both ImageResizer 3.1.5 and 3.2.1 are targeting v2.0.50727</p>
  
  <p>Any ideas on how this could be fixed?</p>
  
  <p>Thanks in anticipation!</p>