Update method

[Exigency]

Just noticed the update method is missing a 'WHERE' clause in the query builder.

public function update($table, array $data, $where = array())
{
(...)
  // handle where clause
    if (!empty($where)) {
        $sql .= " WHERE "; // <-- Needs to be added
        if (!$this->_isAssociative($data) || !$this->_isAssociative($where)) {
            throw new Exception('Update requires $data and $where to be associative.');
        }
(...)
}

Superb class by the way, it's very clean and pragmatic.