updated entities.Fighter to add 'killed'.  this means that the player can be dead, but not yet killed. that way, player can die in other parts of the code, but only be 'killed' once in the player death function
seems to make sense.
tweaks to get the basic game to work again. it was constantly killing the player.
see previous commit on adding entities.fighter.killed. so if player selects battle royale, then player.fighter.alive = False.  then in the main loop, we just check to see if player is alive or not. if not alive, call player_death.
and in player_death, player only runs the death code if it hasn't already been killed.

this feels a bit redundant, but seemed to make sense at the time. maybe I'll change my mind later
added a quickly coded up Game of Life using libtcod