Martynas,
Unfortunately the latest git version is broken for me. At least in libraries/chart.lib.php on line 5 you use a lower case filename which does not match in case-sensitive environments.
Some other points: * Please use curly braces even in situations where they are technically optional. Not: if (is_null($options)) return;
but
if (is_null($options)) { return; }
* Please make sure you properly escape variables you print to the user. $sql_query in tbl_chart.php should probably have htmlspecialchars() In general ... distrust any data you get from the outside.
Most code looks OK though, nice going.