Add mysqli_error_list() that returns an array with errors. Typically only

Add mysqli_error_list() that returns an array with errors. Typically only
one and just one for libmysql. mysqlnd can return generate more than one error
during its work and with mysqli_error() only the last error is being reported.
In the array returned by mysqli_error_list() / $mysqli->error_list, all errors will be found.
The list is reset when the next command is executed