Pull Request Dev_1.0

for L81 - L96, you may rewrite it as : 
```
if ($row) {
    throw new ExistingUserException("message");
}

if (!$this->validate()) {
    throw new ValidationException("message");
}

$where_params = array(
    // params here
);

$db->insert();
```
You do not need the else if parts since throwing an exception will immediately exit the function call ignoring the rest of the code.