update README to contain missing api endpoints; abort execution when no message should be send

MatrixConnection.php

@@ -18,6 +18,7 @@ class MatrixConnection
 		$send_message = NULL;
 		if (!$message) {
 			error_log("no message to send");
+			return false;
 		} elseif(is_array($message)) {
 			$send_message = $message;
 		} elseif ($message instanceof MatrixMessage) {