day and night cycle

Added the dayCycle object to the rm_world
Added code to scr_drawZombie

Zombies can't be seen at night, until they're in the player's line of
sight.
Added code to scr_globalVars

Player now has line of sight.
Added code to hpTrack

The hp bar appears when the zombie appears in the line of sight.
Day and Night cycle implemented

Day and Night has been fully implemented