Update database.php

Varsion 1.0

-Added "$this->con" variable to reference a connection to improve speed and to reference a connection for functions that require one       (ex: "mysqli_insert_id($db->con)").
-Added __construct and __destruct to open and close a connection ($this->con).

Next:
-Will move paging functions to a subclass
-Will create a subclass that uses prepared statements (mysqli OO)
-May create a PDO version