members_changed
Description:
public signal void members_changed (HashTable<Contact,uint> updates, GenericArray<Contact> removed, CallStateReason reason)
  
  The members_changed signal is emitted whenever the call's members changes.
The Contact objects are guaranteed to have all of the features previously passed to add_contact_features prepared.
Parameters:
| updates | GenericSet mapping Contact to its new CallMemberFlags | 
| removed | GenericArray of Contact removed from the call members | 
| reason | the CallStateReason for the change |