modify_contact
Description:
public async bool modify_contact (Contact contact, BookOperationFlags opflags, Cancellable? cancellable) throws Error
  
  Applies the changes made to contact to the stored version in this.
 The call is finished by modify_contact.end from the callback.
Parameters:
| this | 
           an BookClient  | 
      
| contact | 
           an Contact  | 
      
| opflags | 
           bit-or of BookOperationFlags  | 
      
| cancellable | 
           a Cancellable; can be   | 
      
| callback | 
           callback to call when a result is ready  | 
      
| user_data | 
           user data for the   |