rewrite of fire code - second attempt

    temperature of fire is now determined by the amount of fuel actually burned
    fire consumes correct amounts of fuel and oxygen
    nerfed welder fuel to play nice with the new system
    rewrote the fire object process to make it more readable and saner organized
    deleted some now defunct variables
    adjusted the bomb spawner to produce 1-2-5 bombs like it should

I hope this time I have done the pull request right.