defining ground region

Hey!

I fixed something that is not really important but was bothering me: now there's ground tiles only on the playable region! And the ground region is checked automatically! 

I made a video to show how it's done (The speed of the algorithm in-game is obviously faster). I think it's something pretty satisfactory to watch :3

This is not something that's really important because in the future I will probably set the ground regions manually using the level editor, as I was thinking of having different ground tiles in the level.

But for now, I think it looks better. (And maybe a bit slower to start the level. Sorry for that... :P).

The code for the project showcased in the video can be found in my google drive.
Why didn't I created a repository on github? I'm just too lazy to set a repo > <