Add background tile and tile color tinting to Platformer2D

[cacticrown]

Each Tile now has a ColorTint variable that defaults to white. I added a passable Background Tile that is defined in the level file using , (Comma). This new tile will give levels more depth.

Here is what it looks like:

[cacticrown]

I forgot to mention: tinting the color of tiles could also be used to get more variations without having to create new textures.

[cacticrown]

accidentally closed it. idk how, but it happened

[CartBlanche]

@cacticrown I know it doesn't affect this PR, but thought I'd let you know I just pushed a fix for resolution independence, for this game. It should hopefully render better on everything from mobiles to desktops now.

[cacticrown]

@CartBlanche That also means we can make the game window user resizeable, right?

[CartBlanche]

@cacticrown in theory yes. Just needs testing to be sure. At worse we can just allow toggling from Windowed to Full screen.

[CartBlanche]

@cacticrown I'll merge it. Only thing is we may need to add a specific tiles that looks "inset" more than it does now. Or maybe see how the shadows were done in the shader tutorial and give the player and enemies some shadows, so they don't look stuck to the wall.