title: Generate MD5 hash from Objective-C object
body: <p>I'd like to generate an MD5 hash for an NSObject:</p>
  
  <pre><code>@property (nonatomic, retain) NSString * name;
  @property (nonatomic, retain) NSString * type;
  @property (nonatomic, retain) NSString * unit;
  @property (nonatomic, retain) NSArray * fields;
  </code></pre>
  
  <p>What is the best way to do so? I've seen examples for hashing from a dictionary or an array, but not from an entire NSObject.</p>