Things to do when I was upgrading CI 2 to CI 3

in manner of my own priority.

1. Delete old system folder and replace it with new one.
2. update index.php
3. Replace config/mimes.php
4. Edit config/config.php
5. update config/database.php
6. copy view/errors from source to your project
7. Rename all classes (Controllers/Models/Libs) Ucfirst-like using with powershell command.
8. fix appeared bugs
9. …
10. …
11. profit

yea, it still suck.