Added typedef's for the blocks

[dglancy]

For folks who don't like to do inline blocks, these typedef's are helpful to define the success and failure blocks upfront.

Example of how I would use them:

• (void)requestSession {

  RequestSuccessBlock successBlock = ^(NSData *data, NSURLResponse *response) {
  DLog(@"success");
  };

  RequestFailureBlock failureBlock = ^(NSData *data, NSError *error) {
  DLog(@"failure");
  };

  NSString *url = [NSString stringWithFormat:SOME_URL , [self email], [self password]];
  NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL: [NSURL URLWithString: url] cachePolicy: NSURLRequestUseProtocolCachePolicy timeoutInterval: 60.0];
  [NSURLConnection asyncRequest:request success:successBlock failure:failureBlock];
  }