Add dc_event_emitter_close() API

dc_event_emitter_close() can be used to terminate
event loop from another thread without dereferencing the
context which may be in use by the event loop at the same time.

deltachat-ffi/deltachat.h

@@ -5201,6 +5201,15 @@ dc_event_t* dc_get_next_event(dc_event_emitter_t* emitter);
 void  dc_event_emitter_unref(dc_event_emitter_t* emitter);
 
 
+/**
+ * Closes event emitter object.
+ *
+ * @memberof dc_event_emitter_t
+ * @param emitter Event emitter object as returned from dc_get_event_emitter().
+ */
+void  dc_event_emitter_close(dc_event_emitter_t* emitter);
+
+
 /**
  * @class dc_accounts_event_emitter_t
  *