Updating the visuals for the game: pixel art.

[Nebulean]

The visuals were messy, so this pull request will change the visuals to pixel art.
I am working on it.

Todo:

• Players
• Negative/positive balls
• Ring -> Still not perfect
• Powerups
• Background
• Main menu
• Tutorial (not the priority)
• Replace fonts
• Electric field sprite -> Done, but not implemented.

Issues:

• The trails are slightly too big, the balls are smaller.

[Nebulean]

The first version of all the sprite are now ready (except the tutorial which isn't on the branch yet).
I am open for remarks and critics. ^^
(Except for the ring, I know it is ugly for now)

[Mojert]

The sprites are pretty good ! I'm especially found of the explosion when the ball goes out of bounds. However I have two problems:

• I don't think that not allowing to resize the window fixes issue Fix the fullscreen problem #28. It would be better to allow it. Since it's its own issue and this pull request is about pixel-art maybe that untying the two would be the best.
• The sprite for the electric field should be changed too.

Moreover we still lack a sprite for the magnetic field and the electric field's is only a rectangle even though the effect of the field extends beyond the rectangle. I didn't include those in the check list since these may require their own issue.

[Mojert]

The electric field extending beyond the rectangle is a bug so forget this remark ^^

[Nebulean]

The sprite for the electric field was added, but not implemented as I don't know how to do it without breaking your code. See #38 .

Regarding the resize problem, it is just a temporary fix don't worry. ;)

[Mojert]

Everything seems good to me !

[Nebulean]

Everything is patch, the branch will now be merged to master.