Move all bullet-related functions into one place

Rather than cluttering up main, we are moving all the bullets into
one place, and requiring it.
Use : instead of . to pass self into metatable
Bullet is being updated and drawn and collided

A lot of refactoring and rearrangement

I have passed in necessary information like playerCoords and got
the bullet firing, colliding with objects, but need to test whether
it can hit other players. I was however able to hit myself, so it
must be working.

Remove unused Sprite

Though it might make sense to create Gamelost.Sprite.Bullet and Gamelost.Sprite.Player?

Rename sprite to sprites

More cleanup
Merge pull request #115 from alanjcfs/feature/cleaner-sprite-class

Feature/cleaner sprite class