Upgrade From Version 2.1.3 To Version 3.1 or 4

Hello, version 2.1.3 wont work on PHP 7, as for the upgrade, it is easier to upgrade to 3 (not that radical of a change) but i would recommend version 4.

It may not even be that much work, pretty much the "top" of the files (Controllers, Models, etc) changes (check provided examples on downloaded framework).
The calling of methods (for databases for example) change from like:
- $this->db->order_by("x"); to $this->db->orderBy("x");
- $this->input->post is now $this->request->getPost
- $this->load->model('model_x') -> $model = new \App\Model\Model_x();
- etc
You can probably do most of it with a Find and Replace (just make sure you re-check).