Added a gun to the game

Added a gun to the game and little changes here and there with comments
and neatening of vars.
Updated changelog.lua

Added a list of all the new changes to the changelog screen in the
options menu.
Bullets now de-spawn from player distance

Once bullets get a certain distance from player they de-spawns. Instead
of them going off screen and de-spawning like they were before which
made a bug that wouldn’t let you shoot when you moved 200px away from
spawn with the camera.
Merge branch 'thomas-changes'