Revert "added changes to bullet prefab"

This reverts commit c2709de96c50588bddb32415eedceb82a642b8ac.
Revert "Revert "added changes to bullet prefab""

This reverts commit d51141343fdd2aa2eb93df82232cb12aed615331.
Added rudimentary camera following
Added limits to ship movement vertically
Updated camera to have a constant horizontal scrolling
Finished the camera tracking for vertical motion
Added rigidbody to asteroid and bullets so OnTriggerEnter could work. Asteroids can move now. Added bullet1 tag
Added attack_power on bullets so it doesn't just take a single hit to destroy an asteroid. Also, asteroids therefor have HP.
Added asteroid tag. Made it so now bullets are destroyed when they hit an asteroid
Made ship faster for demoing
Updated README and made the ship fire 3 bullets instead of 1