accept
Description:
Asynchronously requests to accept the incoming call.
Call objects can only be executed once.
When the operation is finished, callback will be invoked in the thread-default main loop of the thread you are calling this
      method from. You can then call accept.end to get the result of the operation.
See accept_sync for the synchronous, blocking version of this method.
Parameters:
| this | 
           A Call.  | 
      
| cancellable | 
           A Cancellable or   | 
      
| callback | 
           A TaskReadyCallback to call when the request is satisfied or   | 
      
| user_data | 
           User data to pass to   |