title: how convert RKObjectMapping (Reskit) to json string?
body: <p>I have the following code:</p>
  
  <pre><code>NSString *url =     @"http://mysite.com"
  RKURL *baseURL = [RKURL URLWithBaseURLString:url];
  objectManager = [RKObjectManager objectManagerWithBaseURL:baseURL];
  objectManager.client.baseURL = baseURL;
  objectManager.serializationMIMEType = RKMIMETypeJSON;
  
  NSString *token = @"Token is getting from rest API"
  [[objectManager client] setValue:token forHTTPHeaderField:@"token"];  
  
  RKClient *client= [objectManager client];     
  RKRequest * therequest = [client requestWithResourcePath:@"/create"]; 
  
  
  [therequest setHTTPBodyString:@"{user:user}"]; //Here receive a JSON value
  [therequest setMethod:RKRequestMethodPOST];   
  [therequest setDelegate:self];                               
  [therequest send]; 
  </code></pre>
  
  <p>This code works fine... but I have a problem, I need to send to Rest API a JSON object (like String) and I have a RKObjectMapping with the values that should be sending to Rest Api.</p>
  
  <p>It is possible convert a RKObjectMapping to JSON?</p>