Initial support for sync

Only sends the sync, does not do anything with the response yet.
Handling the response will be implemented in the next several commits,
piece by piece.

FossilOrigin-Name: 17e299f073f39e55dfe0b8a4bd1b34c8529400138d147df5a7229336df6ba04f

src/MTXClient.h

@@ -142,6 +142,14 @@ typedef void (^mtx_client_room_join_block_t)(OFString *_Nullable roomID,
 		       storage: (id <MTXStorage>)storage
     OF_DESIGNATED_INITIALIZER;
 
+/**
+ * @brief Performs a sync.
+ *
+ * @param block A block to call when a sync was performed
+ */
+- (void)syncWithTimeout: (of_time_interval_t)timeout
+		  block: (mtx_client_response_block_t)block;
+
 /**
  * @brief Logs out the device and invalidates the access token.
  *