tabline: Cache title as tablocal variable

autoload/airline/util.vim

@@ -1,6 +1,9 @@
 " MIT License. Copyright (c) 2013-2016 Bailey Ling.
 " vim: et ts=2 sts=2 sw=2
 
+" TODO: Try to cache winwidth(0) function
+" e.g. store winwidth per window and access that, only update it, if the size
+" actually changed.
 scriptencoding utf-8
 
 call airline#init#bootstrap()