Make ENDL optional like ENDSECTION (#1538)

Add warning for `LOAD` without `ENDL`

contrib/zsh_compl/_rgbasm

@@ -26,6 +26,7 @@ _rgbasm_warnings() {
 		'shift-amount:Warn when a shift'\''s operand it negative or \> 32'
 		'truncation:Warn when implicit truncation loses bits'
 		'unmapped-char:Warn on unmapped character'
+		'unterminated-load:Warn on LOAD without ENDL'
 		'user:Warn when executing the WARN built-in'
 	)
 	# TODO: handle `no-` and `error=` somehow?