Rewrite and improve engine

[zabidenhtf]

Im started branch https://github.com/zabidenhtf/Li-Ri/tree/engine_test and I'm on this branch fully rewrited engine on OpenGL, also added modern C++ stuff. I'm will update new engine (Im planing add rotation of quads), and I'm will fix bugs

[petitlapin]

on my side, I'm not interesting by rewriting the engine, so even if there is a PR with all the changes, I probably won't accept it.
The main goal of Li-ri was to port Ri-Li to a more recent SDL version and android, it was not to do a complete rewrite.
I welcome improvements but a full rewrite is too much for me :).