REST CI & Flash Inputs

Here's my humble support for CI.

This changes provide a way to map a request through different controller methods, based on `$_SERVER['REQUEST_METHOD]`. Allowing now to write code like:

```php
<?php 
class Cont extends CI_Controller{
    public function get_index(){
        echo 'Im a *GET* request handler';
    }
    public function post_index(){
        echo 'Im a *POST* request handler';
    }
    public function put_index(){
        echo 'Im a *PUT* request handler';
    }
    public function delete_index(){
        echo 'Im a *DELETE* request handler';
    }
}
```

Also added the ability to flash input through requests via Session Class. This feature is available with every session handler except for cookie because of cookie size limit.

For Example: 
```php
<?php 
// [...] some controller ...
if( ! $this->form_validation->run()){
	$this->form_validation->flash_input();
	redirect(site_url('form/uri'));
}
```